Moss Bross is good, and if you haggle them with the prices, there'll reuce it for you, at least they did for me
My brother got his first suit for an interview from M&S (he got the job!). Although he now gets his suits made-to-measure from Ozwald Boateng on Savile Row, he still does have some suits from M&S's Autograph collection, where designers make the suits for M&S.
For an interview, if you only want to spend between £100 and £200 on a suit then i'd advise M&S. There are some slight differences between tailored and suits from M&S, but for an interview no one will care that much. However if you want to, you could buy a good quality from shirt from somewhere like Thomas Pink, which can make all the difference to a suit.
ok, buy a suit from a reputable but affordable store then find a tailor who ill re-fit it to you.