I've just had a look through Warplanes of the Third Reich, as well as the Harleyford Me 109 A famous German Fighter. Neither has the photograph the OP mentioned.
However, Harleyford does mention that th '109 prototype flew with a Rolls-Royce Kestrel engine. In addition, pictures of early 109's (B and C models) had a large radiator bath under the nose, so perhaps these might be why the OP thought of the Merlin?
Hope this helps a bit