Anyone can usually appeal for a place at an oversubscribed school, but there is the issue about qualifying for a grammar school.
If the previous qualification is considered to have lapsed, there may or may not be a well-established procedure for late testing.
Dissapointed [sic] Mum had quite a battle with one particular foundation grammar school last year.
It isn't always like this! In Bucks, for example, the LA has a clearly set out policy.
http://www.buckscc.gov.uk/assets/conten ... pt2010.pdf
You will need to contact the relevant admission authority.