crown over the letter R on antique silver teapot

[treboreloop]

does anyone know of a very old mark of a crown over the letter R

[Scotprov]

Is that the only mark?
You can have old French pieces from Paris with this mark, or, more likely, there were some makers out of Hanau, Germany who specialised in repro pieces. You can find out more if you hunt through these forums on them.
If it is a British hallmark, 1813 Sheffield had a crowned R

Richard