Last time I looked I managed to find dinner suit trousers (bespoke, not M&S) in a charity shop for £2. Later I found a Moss Bros rental (I think) jacket in another charity shop for about £6. Of course the trousers fit the jacket didn't. But it's not unlikely to find dinner jackets in your size. Depends which end of town you are. Loads and loads of tailors about, so also not difficult to get one taken in cheap.
Last time I looked I managed to find dinner suit trousers (bespoke, not M&S) in a charity shop for £2. Later I found a Moss Bros rental (I think) jacket in another charity shop for about £6. Of course the trousers fit the jacket didn't. But it's not unlikely to find dinner jackets in your size. Depends which end of town you are. Loads and loads of tailors about, so also not difficult to get one taken in cheap.