The council will have an election services team. Speak to them on Monday. I voted by post and it advised you can take your ballot on the day to your voting station. So even if it arrives on the day he still should be able to make his vote count.
But he lives in Manchester, so can he take it in there, even though he's voring in this constiutency?
Mine didn't arrive either. I called up Haringey electoral services and they sent out another which arrived the following morning. (Or they offered that I could come and collect it in person from the council offices)
Can you get the ballot paper to him before the day? He or you can hand it in at any polling station it says in the instructions. But he does need to sign the paper.
You can also visit our electoral registration office. The office is open 8.45am to 5pm, Monday to Friday.
Alternatively, you can write to the Electoral Registration team at:
The Electoral Registration Office P.O. Box 264 Civic Centre High Road London N22 8LE
The best thing might be a proxy vote which can be sorted out at very little notice - we had to do it once when my partner was called away unexpectedly for work at one or two day's notice.