Having been nearly caught out at the last minute, I thought I would try and state the situation as I found it to forewarn any other first timers.

Cuba will have nothing to do the US or its dollar currency.
They introduced a Convertible Peso (CUC) for foreigners and they have the Cuban Peso for nationals. 1 CUC is worth about 25 Cuban Pesos.

Because of this you cannot get Cuban currency outside of Cuba, ie Post Office, Travel Agents et al, which leaves a choice of cash or TCs.

You have to change your money in Cuba and as this is a Government operation, I was led to believe that the rates are the same wherever you change them. I got the same rates at Holguin airport and the Playa Pesquero Hotel.

Because the Cubans will have nothing to do with the US, they will not accept travellers cheques or credit cards that they decide are linked to the US Banks.

Obviously this means that American Express travellers cheques are NOT accepted, which is bad news for most of us because most of the banks, travel agents and post office only issue American Express TCs.
I have been told that the bureau at the airports will issue usable sterling travellers cheques, but rather than get to the airport and find it was not the case we took cash in 20s.

The Cuban "Banks" do accept Sterling Notes, which were changed commission free, or appeared to be.

According to my UK Bank, the credit cards would be accepted but the Maestro/Switch would not as the technology is not in place in Cuba.
I would not take that as Gospel, so it would be nice if others can confirm or elucidate on what does and doesn't work.

Using the credit card for cash at the "banks" attracted a 10% commission fee.
I intended to pay for the trips on the cc but when it came to it, I was informed that using the credit card would mean that the amount would be converted and processed as US dollars, which may up the cost by as much as 18%.
Naturally, throughout my stay I used Sterling cash and so cannot comment on the accuracy of the extra charges prediction, although I note that we were getting an exchange rate of 60p whereas others have reported the rate as 68p. eg my £20 returned 33.19 CUCs against 29.40 at the higher rate mentioned.

Edited to add:

To the best of my knowledge, the locals cannot use the US dollar and so tipping should be done in the local CUCs, which are also referred to as Dollars, so causing confusion.