Hey Tony,
Welcome back mate. If you'e gonna be in Manchester (my home town, btw), then the easiest gig will probably be the inland site at Ecclestone ('Eccy') Delph - see this link:
http://www.thedelph.com/plans.html
It looks a lot better nowadays, as some of the pics on the above link are out of date, but the site, I believe - and guys correct me if I'm wrong - sports the usual suspects of boat wrecks, cars and I think an APC and Tank! Depth I think now is 20-25 metres. Air on site (don't know about Nitrox) and I can't tell you if they rent kit or not, so you may need to bring your own - fellas, any help here??
Next time you're gonne be in town for more than a day, let us know and we can turn up and make a day of it.
Hope that helps mate. Travel safe.