Can I just swap out my 28 tooth rear cassette for a 32 without buggering about with indexing the rear mech again?…both 10 speed BTW.

yes assuming your chain isn’t on the short side its should be a simple swap.

At the most you’ll need to adjust the B tension screw so the jockey wheel sits a bit further down but you shouldn’t need to move the high-low limits

Should be able to – I’ve done it on a road bike going from 25 – 28. Your chain might be a little short but probably not enough to notice in practice.

What rear mech?

Older 10sp road mechs will only take up to 28t so it will depend on the rear mech if you can do this or not.

Also best to change the chain aswell.

Thank you chaps, general consensus (on other forums) is that an 11-32 will work with my reasonably new 105 groupset, the 53/39 chainset is killing me up here in Wales!….it was fine down south.

What BCD is the chainset? You might be able to help the gearing by reducing ring sizes too…