I have a spare phone kicking around that I'm thinking of leaving plugged into my car to provide google maps and spotify.

How much monthly data do you think would be needed?

1pmobile does 2GB for £6pcm or 4GB for £7.50pcm.

Looking for low cost for low(?) data use.

Any other recommendations for cheap sim only providers in the UK?

@bigcalm Smarty offer 12GB/month for £6/month. http://referme.to/3YPXCsx

@bigcalm But actually, I think how much data is included in the plan will turn out to be pretty irrelevant, and the cheapest you can find will be fine. Can't you get usage stats for these apps from your existing phone?

@mavit usage stats might well be the key to understanding before committing to a plan. At least for maps.
Spotify and such are in use outside of the car, so less accurate here.

@bigcalm But at least you get an upper bound, which might be sufficient to answer your question.

If you're not using the phone's storage for anything else, you can pre-download maps for the whole of UK.

Watch out for software updates, though, if you never bring the phone onto an unmetered network.