If you have any holiday entitlement owing to you, you could ask that that be offset against the notice period, ie if you have "earned" 8 days holiday up until the date of your resignation and taken none of it, you could work 31 minus 8 days as notice period. A lot depends on your Contract of Employment and they may have the right to refuse to allow you to do this and pay you your owing holiday entitlement in your final pay packet.
Failing that, I would work the 28 days and then just leave, and personally I would think they would be very unlikely to sue you for breach of contract over 3 days!