I went to see the vet this morning. It was originally going to be for the 'snip' but Daddy has been having a rethink in view of comments from various sources (including here!). So I had my annual innoculation instead and Daddy spoke to the vet further. We saw a different one this morning than before and his view was that it was up to Daddy as to whether to have me 'done' or not - he was not dogmatic about it. There are medical advantages, in particular there are lower chances of prostate and testicular cancer. (However, it is more important to have a bitch spayed.) He also said that the summer would be an appropriate time, as that is when I would be mature. Daddy is therefore going to think about it further over the next few months.
The vet also said that I am now old enough for longer walks - yippee! Most of my growth plates have now closed. Here is an information sheet that Daddy found on the subject: http://www.yourvets.co.uk/html/pdf/Factsheets/Dog/24_265463.pdf.