I know about the requirements concerning proof of funds for UK immigration purposes. They are well laid out in the answer to Can I convince embassies to accept my overpaid credit card as a proof of funds. My question however is not covered in the answer in the linked question.
One requirement is that the money is in liquid form and actually available to the applicant.
I will be traveling to the UK with bank statements and everything showing the provenance of the funds in my account etc. However I will not be carrying physical cash more than £20, I hate carrying cash and for even the smallest transactions I use credit cards, partly to accumulate points, the protection and the exchange rate.
For the UK, my question is will carrying a debit card linked to my accounts be considered liquid enough and a proxy for cash? What about a credit card? Note that I am not using the cards as proof of funds, my bank statements etc cover that. I am only using them as proof of liquidity. I am concerned because the immigration officer kept asking me how much cash I had on my previous visit although I had shown him credit and debit cards. I know for the Schengen areas credit cards are acceptable.