It is more than likely an Elster water meter - I was a consultant for them not so long ago - they used to make all these meters in Luton but it has all been outsourced to Slovakia now - They had lots of problems with the chambers in the water meters on some variants as they have tried to eliminate any mettalic moving parts - there is also a vary small filtering device within this plastic chamber that is designed to filter out grit etc, if partly frozen water is clogging this then the brass housing will not heat up sufficiently to melt it .
Even if it isnt an Elster meter they will all have fairly similiar internals.
I would keep on trying to heat the pipes and insulate the meter as that will help but you should report it to the water board as it sounds like the water is freezing before it gets to the meter.
Hope that helps
Darren