Hi

Doing up a bike for a work colleague. Its got 27 x 1 1/4" tyres. They seem few and far between in a 'slick' tread.

Are they known as another size at all??

No, it's a unique size and annoyingly different from 700c.
Continental still do some decent 27 x 1 1/4 tyres. Alternatively you can change the wheels for 700c and use long drop calipers which *should* provide enough adjustment for the brakes. I did that with an old Dawes tourer which I did up for a mate.

I reckon I'll just go with the Michelin World Tour tyres I can get pretty easy – not slick, but ok considering the rest of the bike!

Bontrager do good slick 27×1 1/4.

Schwalbe do some-we use quite a few. They are common on the 'why wont these bikes die' edinburgh commuters.

I got some Continental Ultra Sport's in 27" from Wiggle.

Virtually slick (just a small u shaped tread on the shoulders) with black sidewalls

Yeah, they're available, but not for £6 like the michelins!!