Cameo White from Sanderson is a really lovely warm white, I used to have it everywhere instead of brilliant white in an older house. It isn't yellowy. Don't know if you can get it from B&Q but I think you can order it online.
I had timeless in a previous house and it is on the greyer end of white but I found it neither grey enough or white enough for me but that is very definitely a personal taste as I know a lot of people really like it.
If you wanted to go slightly more grey than white (which it sounds like you could with the colours you describe) Dulux Dusted Moss 2 is lovely, looks fab with white but isn't too dull or drab. There are some lovely google images of where people have used it if you wanted to have a look.