Holy Trinity Church has regular organ recitals in the evenings. In October this will involve accompaniment by a choir and orchestra, for selected works by Mozart, including Requiem.
Going from memory I think it's on the 17th at around seven / seven-thirty, and costing five quid. If anyone's interested I have an email address somewhere to contact for more details
p.s. would possibly be a good idea to meet in a pub either beforehand or post-recital. I'd suggest Ye Olde White Harte or the Mission, but I haven't been to either on a Monday night.