Be very very careful about inspecting the roof for small leaks. If there are any they will soak the battening and rafters and you wont know about it until it is too late.

I would not think that you would be able to get a grant as they would advertise this if they were available -- possibly a non approved insulation system?

Renothern is blooming awful stuff - it traps moisture against the battens, encourages rot and ensures that the slates/tiles can never be used again. I know it's a personal thing, but I think the developers of Renotherm should face a class action for criminal damage! Most local authority conservation officers will tell you not to use it on older properties for those very reasons.
As for grants, you may be lucky and find a local authority still giving out grants for insulation, but it has tended to be for cavities and for 'traditional' fibre batts in the attic rather than for non-approved and potentially destructive spray-on treatments. These days, however, most LAs are so strapped for cash that the grant allocated has shifted to the HEAT project, funded by the EU, and even that is now reining in the purse strings.