Great coverage in the area, good reliability, £5 per month might give you all you need, £8 pm most probably would.
Do you have a Virgin Landline? If so there is an app to link your mobile calls to your landline minutes when you're on wifi. Obviously no advantage if you're not.
I kind of liked...
I'm with Virgin SIM only and had no problem in Brighton and Hove, or elsewhere for that matter. I think I'm on their cheapest sim only, 150mins, 500mb, unlimited texts. It's been fine. I did switch to Virgin from Giffgaff as I did have coverage gaps that my wife didn't who had a Virgin sim...