Can i have some advice please on when and how to prune my two large lavender bushes. They are new to my garden this year but very big and in two large pots which are too big to move or store. I want tto avoid them getting straggly and woody.
I prune just after flowering and don't cut into the old wood.
I do the same as KEF, cutting as far back as possible without cutting into old wood. However, it's too late for you to do that now - 'in the old days' it used to be recommended to prune lavender in the spring, so I see no reason why you shouldn't prune yours next spring - say April - they might flower a little later than usual, but at least you'll have tidier bushes.
Then trim back again after flowering
Thankyou all, I do still have some fresh flowers on plants so maybe I should prune these?
A lot depends on what lavender you have. Musntead and Hidcote are hardy and will survive anything the British winter can throw at them as lo,g as they are well drained and their roots don't get soggy and rot. As mentioned, lavenders in pots may appreciate a layer or two of bubble wrap roun the pot to insulate their roots from cold but the main theing is to make sure the pots are up on feet or bricks to maintain good drianage.
Leave the flowers. They'll be fine. Prune the plants in spring cutting back to the base of the flower stems and a wee bit into the foliage but not as far back as borwn wood as this will not regenerate. Next summer, prune back once flowering finishes and this will stop them becoming leggy and straggly.