If you are not desperately in need then I recommend looking online. We bought a Khyam QE tent from outdoor action ltd and they delivered it within two days. Little trekkers for kids stuff are quite good too.
To be honest I was tempted to say "how dare you not support a perfectly good local business that people come from all across north London to visit"... but obviously I'm a bit price conscious too.
Opposite for me with Nomad. Find their selection very narrow. Have always gone in determined to purchase but come away empty handed. Internet every time, especially with tents.
Not really local, but the best place for cheap camping gear by far is Decathlon. You can view their stock online here http://www.decathlon.co.uk/ , but (annoyingly) they don't sell online. The nearest store is at Surrey Quays. It's a long way, but worth it.