OK. Details please, and I'll write that collation :-)

you need to add dropped letters (by infering them from a UK dictionary)
and take as equal any letters within a couple of keys on a UK keyboard
and potentially transpose letters if I'm typing faster with one hand
than the other. If I'm typing on a US keyboard you also have to
(potentially) replace any character by the character that appears in
that position on a UK keyboard. That just accounts for bad typing, if
you could also correct spelling errors (ie mistakes in my head, not by my
fingers) that would earn extra bonus points.