JodyLea, swimsuits are a bugger to get when pregnant. I used old slightly larger one for a bit then got a maternity one around 5 months. I think the web is the best bet, although if you're in the NW London/Wembley area Mammas and Pappas Brent Cross (by the Holiday Inn, not the main centre) might have some stuff. Otherwise Mothercare and John Lewis Brent Cross (main centre) aren't bad.
Clothing-wise, depends what you wear most and what you're willing/able to spend! If you wear suits for work, for a while you can get away with cheap larger size non-maternity tops (white T-shirts from Primark or TK Maxx) and normal suit plus a belly band to cover up unzipped skirts and trousers (and you can get a little waist extender - a stretchy loop to go over your buttons; or just be cheap like me and use a strong knotted rubber band or knotted pony tail band). Later on you might want to invest in a proper maternity suit then keep for next one or sell on?
If casuals for work the usual suspects (M&S, Mothercare, Top Shop, Dorothy P, Gap) do some ok basic trousers and dresses.
Or look for sales stuff in the higher end shops you see advertised on MN (Isabella Oliver, Crave). Seraphine are nice too.
Jeans-wise: I have a range of sizes as last time, after the baby, maternity were too big and normal size too small. For now, I'm into larger size normal. But maternity jeans and trousers are luuuuvely for the tummy when all else gets too tight. TopShop materity jeans are quite nice but do bear in mind your figure and where you tend to put on weight. If not on your legs and hips, you can buy what fits on them now. If, like me, you have big calves, thighs and bum, remember that you will get significantly bigger there (sorry) so get something with a little room to grow and stay away from skinny jeans!