P11d(B) penalty

When completing a clients accounts in December i realised i had not filed the P11d(b) for the company as the director had started to receive a car benefit  during the year ended 5th April 2011.I was aware of it was required as had previously filed a p46 car i simply forgot, we had not however indicated on the p35 that p11d would be issued.

Having paid the outstanding Class 1a liablity of £473. I have now recieved a penalty determintion for the late filing of the return of £473 (reduced from £600).

Do i have any grounds to appeal, especially in relation to the size of the penalty,