At the supermarket checkout the girl said, 'that's twenty five pounds and one pence please'. This is a very common error. I remember Gordon Brown in his budget speech saying beer (or cigarettes) would be increased by one pence. It is so irritating. Does nobody say penny any more? Penny singular, pence plural. Not dufficult is it?
Re 'One pence', I remember being aghast to hear the PM, the Boy Blair, use the expression in a parliamentary speech. It can only be either Nursery level humour, or downright ignorance... akin to wearing socks on both foots.
My English grammar never was that good, so most of these pass me by, except "more dearer" etc (whatever the term is for this type of error) Oh and by the way I never don't put both foots into each socks.