It adds: "One of the best ways to keep thieves out is to use nature's own defence mechanisms to stop intruders.  "A barrier of prickly hedge may be all the protection you need around your property."  It then lists all 30 plants, stating 'Here are some suggestions for plants to use', adding jokingly: "We have tried to identify the plants mentioned by their correct botanical name, but we cannot guarantee that the plant you buy will not grow into a small, fragrant flowering shrub with no more thorns than a daisy."  The first 16 plants on the list give detailed description of the plants and is as follows;  1 - Creeping Juniper - Juniperis horizontalis 'Wiltonii' - Also known as 'Blue Rug' because it has long branches and its prostrate shape forms a flattened blue carpet. It has a thorny stem and foliage.  2 - Blue Spruce - Picea pungens 'Globosa' - Rigid branches, irregular dense blue, spiky needles. Height 1-1.25m x 75cm - 1 m. Slow growing. Moist rich soil.  3 - Common Holly - Ilex agulfolium - Large evergreen shrub, dark green spiked leaves. Large red berries on female plants only. Any well drained soil. Plant with garden compost and bone-meal.  4 - Giant Rhubarb - Gunnera manicata - Giant rhubarb-like leaves on erect stems, abrasive foliage. Can grow up to 2.5m high. Plant by water-side for effect.  5 - Golden Bamboo - Phyllostachys aurea- Very graceful, forming thick clumps of up to 3.5m high. Less invasive than other bamboos. Hardy. Young shoots in spring.  6 - Chinese Jujube - Zizyphus sativa - Medium sized tree with very spiny pendulous branches. Leaves glossy bright green. Bears clusters of small yellow flowers.  7 - Firethorn - Pyracantha 'Orange Glow' - Flowers white in June, with bright orange-red berries. Thorny stem. Height 10-15ft. Suitable for north or east-facing wall or as impenetrable hedging.  8 - Shrub Rose - Rosa 'Frau Dagmar Hastrup' - Excellent ground cover, pale pink flowers, very thorny stem. May to September. Plant with garden compost and bone-meal.  9 - Pencil Christmas Tree - Picea abias 'Cupressina' - Medium-sized tree of columnar habit, with ascending spiky branches. Attractive form with dense growth. Avoid dry chalky soils.  10 - Juniper - Juniperus x media 'Old Gold' - Evergreen. Golden-tipped foliage. Prickly foliage. Height 2ft. Spread 6ft. Low growing. Excellent ground cover.  11 - Purple Berberis - Berberis thunbergil 'Atropurpurea'- Rich purple foliage. Thorny stem. Medium-sized deciduous. Any soil sunny position.  12 - Mountain Pine - Pinus mugo 'Mughus'- A very hardy, large shrub or small tree, with long sharp needles, of dense, bushy habit. Leaves in pairs, 3 - 4cm long, rigid and curved, dark green, cone.  13 - Blue Pine - Picea pungens 'Hoopsii'- Small to medium-sized tree, spiky needled stem, densely conical habit, with vividly glaucous blue leaves. Likes moist, rich soil.  14 - Oleaster - Elaeagnus angustifolia - Small deciduous tree, about 4.5 to 6 m (15 to 20 feet) high. Smooth, dark brown branches that often bear spines and narrow, light green leaves that are silvery on the undersides. The flowers are small, greenish, fragrant, and silvery-scaled on the outside, as are the edible, olive-shaped, yellowish fruits, which are sweet but mealy. Hardy, wind resistant, tolerant of poor, dry sites, and thus useful in windbreak hedges.  15 - Blackthorn - Prunus spinosa - Also called Sloe; spiny shrub. Usually grows less than 3.6 metres (12 feet) tall and has numerous, small leaves. Its dense growth makes it suitable for hedges. White flowers. Bluish-black fruit is used to flavour sloe gin.  16 - Fuschia-flowered Gooseberry - Ribes speciosum - Fruit bush, spiny, produces greenish to greenish-pink flowers in clusters of two or three. Extremely hardy, thrive in moist, heavy clay soil in cool, humid climate.  It then lists a further 14 plants, stating 'In addition, the following thorny plants can also be considered....Aralia, Chaenomeles, Colletia, Crataegus (including hawthorn/may), Hippophae (sea buckthorn), Maclura, Mahonia, Oplopanax, Osmanthus, Poncirus, Rhamnus, Rosa (climbing & shrub roses), Rubus (bramble), Smilax Prickly ash (Zanthoxylum).  The advice continues, stating: "Although they will take some time to grow, the end result justifies the effort. They should deter even the most determined burglar.  "Hedges and shrubs in the front garden should be kept to a height of no more than three feet in order to avoid giving a burglar a screen behind which he can conceal himself."
The Metropolitan Police has published a list of 30 plants that can help   homeowners protect their gardens from thieves, including giant rhubarb and   gooseberry bushes.