Short answer: no. In December I had to pay £22+ for an exchange 6Kg. Calorlite but had no choice.
If you can tolerate the weight of the standard bottle there are other national gas suppliers of 6Kg considerably cheaper than Calor, but you have to pay the up-front 'hire' charge first time round.
Down in Spain now and if you can buy a bottle - not easy without a fixed address etc. a 12g butane cost less than 11 GBP.
One idea is to go electric as far as you can = you are probably paying for the EHU anyway - here the Lidl 1kw fan oven is almost universal, plus a micowave, and electic hotplate or induction hob. (Limited to 6 amps per EHU here - should be much easier in UK)
Caravan Battery we think is dead even though we have solar