Nobody wrote:
Can anyone recommend a good supplier/shop of such items in North/North
West London? Any recommendations as to brand/model? To fit a
600mm space under the hob/worktop.

We like the Stoves cookers :

http://www.stoves.co.uk/Built-in-ovens_c6.aspx

and have one of the 900 high Rotostar double gas ovens built under a
work surface.

The one I have has just gone west :-((

As for suppliers, they're mostly box shifters these days...