I was wandering through M&S buying my dinner last night and saw this deal. I'm desparate for a new suit, so ended up buying two £149 suits and saving £75 or so.
To qualify, you can buy a suit under £150 if you buy an extra pair of trousers, or two suits - as long as the total comes to £150 or. As an FYI, there are quite a few suits in their Autograph and Performance range which are £149, so maybe use it as an opportunity to get a couple of suits or grab and extra pair of dinner jacket trousers because your current pair no longer fit your waistline!
I beleive you can get 3% cashback on Quidco as well - http://www.quidco.com/high-street/high-street-fashion/marks-spencer/
The sale started on Monday 21st and ends on Sunday 27th. I bought mine in the massive Oxford Street store and they were already out of my size in a few blazers, but you can still order them into the store or buy online and get your cashback. I opted to order in store, so I know the suit won't have been tried on by God knows how many people in-store.
Suit up people...