Seeing as you seem to know what you are talking about and are in the UK, where would you recommend for a suit for ~£400-£500? I need another suit for work, the one I have at the moment is from Moss Bros and I'd like a step up. There are shops like Boss, Ted Baker and Ben Sherman where I'm moving to that I need to check out but I imagine they are a bit overpriced?
Hmm. Depends really; are you planning to wear it just to work (as literally a workhorse suit, i.e. once it's worn out, you'll just bin it)?
Or do you want to be able to wear it to work and then maybe use the trousers/blazer as separates to wear with other things for a less formal/off duty look?
You can get a good quality suit from Paul Smith, and for your budget there are 3 ranging from £485 to £515.
However if you want the suit to be a bit more versatile and have it longer lasting, then you could consider getting a special order suit from Anthony Sinclair (savile row). It's a little higher than your current budget at £750 (pre vat), but it's one step away from full on bespoke and you have the choice from an almost limitless number of cloths, style/cut (i.e. tapered trousers, flared, straight leg, belt loops, side adjusters, double vent, single vent, wide/slim lapel, notch/peak lapel etc) and finishing details. It's also made in England and has a delivery time of 6 weeks, so given the time, it's worth considering depending on if a) you think it's worth it, and b) your situation, use of suit etc.
Definitely check out those stores that you mentioned nearby. I've never bought a suit from those stores, so I can't comment on their quality, comfort, longevity etc.