Why won't ALDI accept credit cards?

In the UK Aldi are a leading discount supermarket, they retail brand name and own label products cheaper than the big four Supermarkets, in order to be competitive they need to keep their costs low, credit card companies charge retailers a fee, usually 2% to 3% of the transaction debit cards do not charge this fee, so Aldi will only accept Debit Cards or cash to keep costs low.