Inappropriate billboard advert complaint

Letter sent to MP...

Dear John Cryer,

I wanted to make a complaint about a billboard advertisement at the bottom of my road which features material (a woman scantily clothed with the caption "Ooh la! la!") quite inappropriate I feel for the place it has been placed. I tried looking it up but I am not sure who I should direct my complaint to. Not sure if you know? Would it be the Advertising Standards Authority or someone in the council perhaps?

I apologise if this is not the kind of thing I should be contacting you for.

Yours sincerely,
Adil Hussain

... Awaiting his reply.