The official notice displayed outside the local town hall and on the council's website includes the number of spoilt votes cast. TV and the newspapers choose not to report this.
I was also once told by a prospective candidate that candidates are actually shown the spoilt ballot papers.
I never used to vote, because I have no belief in the ability of any of the parties to serve my interests as I would wish. Hopefully spoiling my ballot paper (I scrawl the words "none of the above" across it) they will see this.
Towards the end of the count, the Returning Officer will call the candidates and/or their agents together to examine all the spoiled papers. The counting staff are under instructions to set aside any ballot paper incorrectly marked. The RO will show each spoiled paper to the candidates who are free to question whether it is actually spoiled or valid. This must be agreed by all the candidates but the RO has the final say.