While I suspect Mr. Bangert of a slight over elaboration, they certainly do grow very big indeed, but this depends on the variety of carp. The ones that can be found in UK waters are not as big as they can get I believe.
The king Strain of carp which are commons, mirrors, leathers and linears can probably grow to around 60lbs in the UK, although the british rod caught record 'Mary' as been caught at several weights over the years to over 56lbs.