Many thanks for all your replies folks .. provides me with food for thought.
I need to either do a pre-plan (though the opinions here are giving me doubts about taking that option) or deposit enough savings in an A/C to cover today's funeral cost in the hope that interest earned will cover inflation. At the moment my estate (less the home/contents which will go to my partner) is more than sufficient to fund a decent funeral, but that may not be the case in a few years time. By investing that money my remaining beneficiaries will lose out, but at least they won't have to pay my funeral costs .. they can't have their cake & eat it.
Both my partner & I have already decided on a local funeral director, on the grounds that they provided excellent service for a relative a few years ago, so perhaps I will also ask them for advice.