Thanks Daniel, I'll decide when we get up to the gutter and see how the neighbours' gutter has been dealt with, but I suspect that Acypol will be the answer!
Thanks very much everybody - thats really helpful.
Somebody else mentioned a rubberised paint with fibre reinforcement. Has anybody got any experience of that please?
The guttering on my semi has sectional concrete guttering cantilevered out from the walls. After cleaning thoroughly (sandblasting?) and making good any joints (with mortar?) the gutter will need to be re-surfaced. Help please!