I've found these 2 sites - they sell 3 and 5 litre pots respectively ....
http://www.thelavenderg.co.uk/pricing.htm

http://www.plantswholesale.co.uk/product/english-lavender-hidcote-angustifolia-hidcote-5-litre-pot-C05LAVH30.html

But a warning - plants of that size in pots may be a couple of years old at least - lavenders usually need replacing every 5 -7 years because they become leggy, woody and unattractive, so by buying larger, more expensive plants, you'll get less of a lifespan from them. Planted this time of year, Lavenders grow fairly rapidly.

thanks for the advice i found the plants wholesale one but they are out of stock i have emailed the other site. thanks again!

Yeah, i'm inclined to agree, Bamboo :-/

I 100% agree Bamboo, I grow a lot of lavender and find it grows rapidly from April onwards. Depending on what kind of Lavender you want SJ you can get a lot at bargain prices. Supermarkets especially sell a lot of Stoechas. You could always mass plant it for impact!