The problem is that there's no statutory definition of what a 'criminal record' is. It's generally taken to mean a 'record of criminal convictions', in which case a caution does not create, or form part of, a criminal record.
However, since the creation of the Criminal Records Bureau, a looser definition of 'criminal record' has come about, which means 'information which is held, and can be disclosed by, the CRB'. If this definition is accepted, then a caution does form part of such a record.
There was a similar post just a couple of days ago and you'll find much more detailed information about cautions here:
http://www.theanswerbank.co.uk/Law/Criminal/Qu estion324852.html
Chris