According to Government Statistics 54% of adults now do their banking by internet. Of course that is the proportion of the whole population. In your target customer-base it is likely that the vast majority regularly transfers money by internet. Those customers who keep their accounts in credit and get free banking will be attuned to the idea of making an advance payment to you by internet transfer directly to your bank account.
Until recently all electronic transfers made through the BACS system took 3 days to clear as illustrated by the British Bankers Association. (This compares with 4-6 days for a cheque). The Faster Payments Service which came into being in May 2008 allows electronic payments (usually made over the internet or phone) to be processed in hours rather than days. This new system is being progressively introduced between UK banks only. At first the payments allowed by this method were very small but now typically amounts of up to £10,000 are being permitted.
The Faster Payments Service is therefore the best, quickest and potentially the cheapest way of transferring funds from customers to you. If both parties have free banking there should be no cost.
Not all UK banks can receive a faster payment. Use the checker on this website to find out if your bank can recive them.
This website page lists all the participating banks in the Faster Payments Service.
Even if transfer by Faster Payment is not available a BACS Internet transfer is probably faster than any other method without going to the expense of CHAPS.
Read more at UK Payments website.