The O'Neills on the corner of Carnaby Street is horrific, just about the only place I have walked out of without finishing my food, Central London is a big place with lots of decent pubs that serve decent food I would recommend that you visit http://www.fancyapint.com/
select the area or tube station you'll be nearest to and see if you fancy any of the pubs listed otherwise try http://www.pubfoodguide.co.uk/