According to various (dubious and completely unofficial) surveys, Christmas Eve is the most popular time of the year to propose; guaranteeing lots of friends and family around to celebrate the happy news. So, if you’re feeling the romance at this time of year, we give you our guide to buying an engagement ring.  How do I know what she'll like? (Or he – for the sake of simplicity we’ll stick to the traditional model. Kudos, though, to Tiffany & Co for the first ever appearance of a same-sex couple in its romantic “Will you?” advertising campaign.) If you don’t already feel confident that you know her style, ask her friends, her mother, her sister – but only if you trust their discretion. The last thing you want is for her to catch wind of your plan.  Take tips from her wardrobe and the jewellery she wears. Does she favour classic fashions, minimalist jewellery, label-heavy handbags or avant-garde jewels? Chances are she won’t want to discard all of her existing gems when she slips on this ring, so make sure it complements her tried-and-tested favourites.  In pictures: the best classic diamond engagement rings  How do I find out her size (and is that even important)?As much as she’ll want to wear the ring straight away and never take it off, it’s not the end of the world if you need to get it resized. Usually the jeweller you buy it from will do this for you, unless it’s a complicated antique piece or a very unusual ring, which may require more specialist attention. The easiest way to find out her size is to slip away with a ring she already wears on her ring finger (closest to the little finger), take it to any jeweller and get them to tell you the size. Or, print out a ring sizing guide (bluenile.com has a handy one) to do this yourself.  I have family stones, what's the protocol for getting them made into a ring?Lucky you. Now you can spend a little more on the design and manufacture. It’s best to be fairly certain of her tastes if doing this though, as if the end result goes down badly, you’ve just thrown money down the drain. Also, get the stones properly certified before handing them over to a jeweller if this hasn’t already been done. Anchorcert offers a diamond and gemstone grading service and is backed by the Birmingham Assay Office.  How and where can I design my own ring? Jewellers make their money largely from selling stones and precious metal, so don’t expect Harry Winston to knock you something up to your specifications with Grandma’s sapphires – although it will work with you on something bespoke, but in its style, with its own stones.  If you really want to design your own piece and use your own stones, you need a manufacturing jeweller, not a designer. London’s Hatton Garden is awash with designer-makers, like Heming, which has been around since 1745.  You’d be surprised at how many jewellers – from big name Bond Street houses to small independent jewellers – will help you design your own ring and get it made, but usually you’ll also need to buy the stones from them as well.  In pictures: the best rose gold engagement rings  I want something really bespoke. Where do I go? The high end Mayfair jeweller Jessica McCormack has an entire floor dedicated to exquisite engagement rings, but will also work with clients on creating a bespoke ring – be it an enormous 10-carat stone in a classic Georgian cut-back setting or a something more personal incorporating unique features like secret messages on the shank.  The independent, Notting Hill-based jeweller Lauren Adriana only makes around 20 pieces a year, so getting her to design your engagement ring would be a real coup, although don’t expect anything simple – Adriana’s work is avant-garde, art-deco inspired and not for the faint-hearted.  Plenty of jewellers will design something around your own stones, but if you’re determined that you don’t want any designer input, one of the new direct-to-customer diamond dealers like 77 Diamonds, Star Diamond (whose showroom in Mayfair has some seriously impressive coloured diamonds) will both sell you loose stones and allow you to design the setting.  In pictures: the best unusual engagement rings  What if she doesn't like it? It totally depends on the girl. Either she’ll say nothing, in which case it’s not an issue and you can go on being blissfully oblivious to her wants and needs, or she’ll tell you. Or the look of utter disdain on her face will. It’s not a total disaster. Like most things, there’s always the chance of an exchange, or less likely, a refund – but find out what the deal is before putting cold cash down. And don’t take it too personally. Chances are she has been thinking about what her dream engagement ring looks like forever.  Do I have to buy a diamond engagement ring or can I go for another gemstone? Not only are coloured gemstones having a serious revival, but they’re gaining in value to make them a worthwhile investment. Most women wear their engagement rings everyday, so stick to the harder stones. Diamonds are the hardest, but emeralds, for example, are relatively soft, and not ideal for everyday banging about.  In pictures: the best coloured-stone engagement rings  Do I have to go for platinum? No! Don’t forget that diamonds come in other colours, as does gold. Maison Dauphin, one of the newer fine jewellery houses, does a really gorgeous line in black diamonds set in blue gold (white gold finished with blue rhodium) which would make for an unbelievably contemporary engagement ring.  Glenn Spiro has a range of engagement rings in classic styles but set in beautiful coloured titanium – a pop of vivid colour in a traditional setting. Similarly, jeweller Raphaele Canot has mastered the use of enamel in rings and her OMG series of diamond, gold, and enamel rings in the shape of an open mouth would suit a bride with a sense of humour. Or, sticking to white diamonds and yellow gold, British jeweller Alex Monroe’s new line of Wild Rose diamond rings are a sweetly sylvan option for lovers of whimsy.  Is it okay to buy vintage? It’s okay by me – but is it okay by her? Personally, I find proper antique jewellery hard to beat, and spend hours trawling sites like 1stdibs.com, or looking at the stock of dealers like Lucas Rarities or Symbolic & Chase. But vintage isn’t for everyone. If she can’t walk past Oxfam without gagging, stick to brand spanking new. Gray’s Antiques in W1 is an incredible treasure trove of jewellery dealers under one roof, with thousands upon thousands of vintage and antique pieces on display all the time – a casual stroll through there with one’s beloved and a beady eye out to see which styles light up her face might be wise.  How much should I spend? There are all sorts of myths about having to spend a certain multiple of your monthly salary on a ring, but you know your financial situation better than some random calculation would. The comfort rule is a good one. If you can comfortably afford it, you’re not spending enough. You want to wince just slightly when making that transaction.  In pictures: the best vintage-style engagement rings  I know she wants a one carat diamond - how do I know I'm getting a good price? Diamonds may be a girl’s best friend, but they’re also a commodity with a market value. Subscribers to the Rapaport Diamond Price List can follow their value or work out the wholesale value of a particular stone based mainly on the four Cs – Carat, Cut, Clarity, and Colour. There are plenty of online calculators that will do the same thing, but your best bet is to compare and contrast in the real world. How much is the jeweller next door selling the same 1 carat D-coloured VS1 brilliant for? Shop around, and don’t be afraid to barter.
Choosing an engagement ring needn't be a formidable process. From the style, to the stones and the size, Annabel Davidson breaks down the key details you need to know