So it is my DH's 40th birthday party in a few weeks

[RosaLuxembourg]

We are having a BIG, but informal do, taking over a local cafe for the night and having a disco and buffet.
You think I am panicking about what to wear but no... (I'll do that later)
I asked my DH tonight if he had thought about what to wear for his SPECIAL PARTY
He said that he probably has a shirt or two in the wardrobe that will do.
I said OH NO NO NO THAT WILL NOT DO AT ALL

So ladies help me please - what can he wear to look nice.
He is a freelance journo and lives in jeans and tshirts and has what he calls his LONDON SUIT that he wears for meetings.
I am thinking smart casual here, but what?

Rosa, his party, let him wear what he wants. Yes, that might be faded jeans and a tatty t-shirt. But his do. Put all your energy, and cash, into what you are going to wear. (easy to say when not my DH, I'd be having kittens if I was in your situation. But objectively speaking, I know I'm right!)

under rather than over dressed is always a good plan. and it is his party to he gets to set the bar.

I know you are all right re letting him wear what he wants, the thing is he hasn't thought about it but would probably like a new outfit if I don't make it too hard for him to acquire one - ie steer him to the right shops and gently suggest something or other looks good on him.
He never buys himself clothes and we have been brokish this year so he hasn't got much to fall back on.

Well, check out his wardrobe - it might be he has something hidden away there that you've forgotten about and that'll do. Otherwise, a new shirt would probably lift a pair of trousers he's already got. I swear by TKMaxx for these occasions, but Gap/Debenhams can be surprisingly reasonable. Sort it out quickly one way or the other so you can enjoy the run up to his special day!

For everyday he wears jeans ( blue or black), white tshirts and very plain grey or brown jumpers. For smart he wears a dark suit, plain or stripey blue/purple/green shirts and no tie if he can get away with it.
And he never buys ANYTHING to wear unless his old stuff is completely worn out.

I am thinking maybe new black jeans as you suggested and what sort of top. Nearly all his clothes are from Gap or Next. Where else do men buy clothes from? He occasionally flicks through the Boden catalogue and laughs hysterically at the funny clothes.

He would like that shirt TMMJ. I will show it to him.
I was thinking of taking him on a shopping expedition to our nearest big town (we live in Sticksville). I know there is a Gap and a Next there but where else might he look?

John Rocha and Red Herring at Debenhams are fairly Gap/Next like and they are on-line too. WHere do you live (roughly) so locals can point you at other places (second time I've written that tonight!!!)