House of Fraser normally do a good range of suits that are more "upper end" of the off the shelf range. Most House of Frasers have access to a tailor who can make alterations for very little too. Last one I bought wasn't expensive, about £3-400, but after £20 of alterations to make it fit even better, it looks much more tailored.
I did, many years ago, probably in 1999, buy a machine washable suit from Tesco for £30. Jesus christ, that was bloody horrendous.