Get thee to New Look. Tons of maternity clothes at very reasonable prices. I bought 3 pairs of trousers, 2 shirts, 1 dress and one pair of leggings for about £100. Apparently there is lots of stuff on their website as well.
I also went to Top Shop, but only found 1 pair of trousers and 1 shirt there.
Now I am exhausted. Its very tiring walking around with an extra person inside of you.