Is it too late to buy seed potatoes?

Off you go to find some then. They can go in at the usual planting time, whether they are chitted or not

There is debate about how much difference it makes chitting maincrop spuds. Though a lot of people seem to agree it makes a difference with earlies. Get them bought - they might even be reduced now!

Well, I managed to buy a load of second earlies and they had already chitted in the shop.  Bonus!

Not wishing to dampen your enthusiasm.... but... that may not be a bonus.
Depends on how they have actually chitted. If they are long sprouts already they may be a bit advanced, if they are long white sprouts I would suggest they haven't been kept in the store properly.

If they are nice short sturdy looking green sprouts then you've done well.

Hope its the latter.

Hmm... they are short white sprouts, mostly under an inch long. They look pretty sturdy and are slightly green/purple tinged...hope they will be OK as I bought a couple of kilos!

I'm sure they'll be ok,  less than an inch of growth is  a better situation than some of the posters recently seem to be encountering.

Reasonable amount of light, not direct or excessive in a coolish place and they'll probably be just dandy by the time it comes to planting them out.

Hmm... they are short white sprouts, mostly under an inch long. They look pretty sturdy and are slightly green/purple tinged...hope they will be OK as I bought a couple of kilos!

Stick them somewhere light, with as little heat as possible (but MUST be frost free) they should turn from white to green and if they don't get too warm they won't grow any more / much more.

Either way, plant them when at the normal time.  If the chits are still white / any longer then be very careful when you are planting that they don't get knocked off - longer chits will be more brittle.  However, if they do get knocked off its not the end of the world! the Spud will make some new ones - that just takes a bit longer, and uses up a bit more of the stored energy in the Spud.