Well you would have to omit BT and TalkTalk at least, I expect Sky as well, as they have 12/18 month contracts. I think Post Office broadband is 12 months as well, even though the phone is monthly.
Do you intend to count Entanet resellers as separate ISPs? That could up the count, but is cheating really.
You could include O2 in the list as they have a 30-day getout on both LLU and IPStream.
Excluding multiple Entanet resellers, at best 20, (one day to get a MAC and 8 days BT reaction time), and more likely 12, (average four days to get a MAC plus 8 days BT) with some taking longer for a variety of reasons.
I suppose it would rather spoil the fun if you simply asked
this guy. He seemed to be trying it a couple of years ago.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - IDNet Home Starter Fibre.
Live BQM.
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.