All these people want is to extract money from your bank account.
They want you to pay as much up front, by cash or cheque.
I feel the contract is unenforceable and one sided. The "time of the essence" clause in the contract and the labeling of the goods as "Custom" I think is a obvious breach of some of these acts & regs.
Check out Cancellation Of Contracts made in a Consumers Home Regs 2008.
Also Unfair Contract Terms Act 1977.
Plus the usual Sale of good act etc.
Even the website breaches the UK's E-Commerce Regs.
I suspect the pack of cards is not far away from falling, which from all accounts will leave a lot of people out of pocket.
If your talking up to £5000 then the small claims is the best route. Over that amount could be a bit more expensive.
Good Luck