If you don't need a walk in service, we use Carrington Mortgages UK. Really good feedback - we introduce all our clients (and staff) to them. More knowledgeable in the Scottish market, but I'm sure we've referred clients in England to them too. http://www.carringtonuk.com/contact-us
I think these guys have also opened up further north than their name suggests http://www.london-money.co.uk/ - seem like a nice bunch.
We use these guys. They are based in Manchester (we are in London) but all contact is via phone and our clients have been happy with the service they have received. They've also been happy to provide CPD and updates to advisers in our office.