Can my eldest child contest my will?

These are the only persons who can contest a will in the UK, so yes, your eldest son can:

Only the current or previous spouses; any child or person treated as a child; any person who was being maintained immediately before the death of the deceased or who lived in the same household for two years prior to the death can claim.

Anyone with a legal interest can contest a will. The question is whether they will win or not. If you are concerned, get a solicitor to draw up the will and make it airtight. You may even be able to put in a poison pill that states anyone who contests the will gets nothing.

Anyone with a legal interest can contest a will. The question is whether they will win or not. If you are concerned, get a solicitor to draw up the will and make it airtight. You may even be able to put in a poison pill that states anyone who contests the will gets nothing.

This should be a sticky ! I especially like the poison pill comment.