That’s an odd one 
Smarty £6
1p Mobile £36 for a year unlimited calls and texts only (£3pm)
Vodafone pay as you go top up £5 minimum and I believe any usage triggers a £1 a day charge which also gives unlimited calls and texts
Lebara sometimes offer £2.50pm deals but min 12 month contract.
Three 123 sim if you can find one on eBay.
O2 also used to do a similar deal.
Asda mobile 4p per text min or mb and top up doesn’t expire if you make a text or call every 180 days