A guy at work was complaining that he needed a bike service and couldn't find any shops that would do it as they all had a huge backlog. He said Halfords do it for £17 and I was just wondering what kind of service you would get for that sort of money?

Basically (and it is pretty basic), a serviced bike will have:

Brakes working, gears working, bolts tight, tyres pumped up, bearings not loose/tight, nothing loose/snapped/worn out/dangerous.

IME, '£17 services' (that's a '£15 Checkover' in my shop…) end up at an average of £30-ish once all the parts are factored in.

I think it varies where you go – LBS strips down the drivetrain and cleans them all – re-index, lube, checks over bike etc – Think that was about £50 – that's a full service IIRC.

£17 at Halfords would get you (at a guess) setting up gears and brakes only.

What I know as a service is the above + setting all bearings and truing wheels. Greasing bearings is part of an overhaul.

Stripping stuff down and 'preventative maintainance' comes under the bracket of full/race services – usually £50-£100.

In short, you get what you pay for.

Most cheap services say they'll "check" lots of stuff but then they charge you for doing anything about their findings

Thats more a less what I thought. My idea of a service would be stripping down gears and brakes and relubing etc.
I was going to offer to service the guy at work's bike until he said he had 2 bent wheels, the brakes didnt work and the gears didnt shift properly. He appears to be under the delusion that all this will be sorted by Halfords for £17 🙄