Carl
Damage and annoyance aside,if you really feel that this chap is unwell and therefore unfit to drive,then either contact the dvla or report what has happened to your local station,expressing your concerns.
As mentioned,it's a damage only and you have both complied with the road traffic act regarding your obligations-however having someone who may be seriously ill behind the wheel needs to be explored further.
The DVLA medical unit are very pro-active and due to the possible implications of not acting when informed,they are quite thorough and will revoke a licence pending medical reports.
In recent months,I have reported a couple of people to this unit and have been updated very quickly as to the outcome.
One was an old boy who travelled the wrong way down the motorway and the other was a young chap who had a fit whilst at the wheel.
The former gave up his licence and the latter had his revoked pending further tests.
If you have genuine concerns,It's not malicious to report this,you may be stopping something much more serious down the line.
http://www.google.co.uk/url?sa=t&sou...m90ii1HNH_NL5g