Had mine at 24 weeks cos i wanted to know the gender and could'nt wait any longer, i love my pics so much i have 2 framed in my room.
Dont know where abouts in bristol you live but i had mine done at film star baby in bath, it was so much cheaper then anywhere else i saw and they were so nice and the lady doing it works at st micheals doing the annomoly scans usually. might be worth a look if you havn't booked already