English lavender, (which is not native to England) is more hardy than the French variety and provided it is not too wet will survive the winter, but only in the right conditions. Lavender really hate having their roots in cold wet soil, and it's the wet which is the real problem. To give Lavender the best chance of success choose a spot which is sunny and has well drained soil. To plant Lavender dig a hole about 3/4 inches bigger than the plant you have purchased and tap out the plant from the pot, tease out the roots, which means put you hand in the roots and free a few gently. Water and plant so that the level of the soil from the potted plant is the same as the earth, and firm it in so it's secure and no air pockets.
If your soil is not suited to the lavender requirements, i.e. not well drained, you can help by improving drainage which is best achieved by adding horticultural grit, (sold at all garden centres.) If your ground is particularly heavy, with clay, tending to water log in winter it will be necessary to dig a trench to create a greater area of free draining soil either where you are planting or along side the path to improve the drainage.
If your conditions are not suitable and a long way from the Mediterranean ideals, try Lavandula Angustifolia,Munstead , Hidcote, (possibly the hardiest) and Intermedia. English Lavenders are all described as *** hardy ( explanation about hardy plants) and the French lavender whilst sometimes described as *** is in truth border line in areas of cold and wet winters. If you don't have ideal conditions, with ground which can get waterlogged, but would love to give Lavenders a try, your best chance is careful soil preparation to drain away as much water as possible, or plant in pots/walled garden to create drier conditions. Hidcote is the best chance of success.
If you garden in one of the colder areas of the country, especially if the area/plot is on the wet side the lavender will be unhappy and are better in pots and under glass/sheltered in the winter. If it is a bad winter and the temperature goes well below freezing on a consistent level lavender may well not survive. Lavender plants are in any event a short livedperennial; up to 10 years in perfect conditions but often become leggy, woody and with bald spots after a few years and are best replaced.
Illustrated below is how a lavender can look after a wet cold winter, much of its foliage is damaged . Whilst the lavender will recover, at least in part, it may not look brilliant and if your conditions are cold and wet it maybenecessary to consider what else to grow instead of lavender? If you have no success with lavender because of the growing conditions, but want that type of effect, the next best substitute is Nepeta (Cat Mint) Although often dismissed as a cottage type plant Nepeta is a long flowering perennial which although preferring dry conditions, it is not nearly as fussy as Lavender. It is true cats like the smell when the leaves are rubbed together. Some varieties get quite large, such as six hills giant nearly a metre. Nepeta is a good candidate for the Chelsea Chop to restrain it and make a more compact plant if needed. Nepeta can look very effective when massed together to create a Lavender type effect where the conditions are such that Lavender just will not thrive. If you are thinking about Growing Lavender but realise the conditions are not favourable take a look at Nepeta which is seen grown in many show and RHS gardens. The image below shows how planting scheme using Nepeta instead of Lavender to good effect. Another possibility is to grow Perovskia atriplicifolia, Russian Sage, illustrated below right, which grows a bit taller than lavender, is much loved by bees and far more tolerant of cooler wetter conditions.