Re: Swivel-Eyed Loon alert
You can write what you like as long as you're not identifiable and your actual voting intention is clear.
47 (3) A ballot paper on which the vote is marked—
(a) elsewhere than in the proper place, or
(b) otherwise than by means of a cross, or
(c) by more than one mark,
shall not for such reason be deemed to be void (either wholly or as respects that vote) if an intention that the vote shall be for one or other of the candidates clearly appears, and the way the paper is marked does not itself identify the voter and it is not shown that he can be identified by it.
http://www.legislation.gov.uk/uksi/2006/3304/pdfs/uksi_20063304_en.pdf [The Local Elections (PrincipalAreas) (England and Wales)Rules 2006]