Thanks Nick, Chas and Rich, seems we all agree about it being a scratchbuilt 'interpretation' of a tender. Possibly someone wanted to portray a post war conversion to pleasure cruiser, hence the styling and colour scheme.
Yes, the sheer line is quite curved, it isn't distorted by the pic. It seems to have been quite well built it's a sturdy little thing. It has an old 540 type of sealed can motor but there's no sign of any radio gear ever having been fitted. Oddly though there's no ratchet or friction type of thing on the tiller arm, though there is a small hole on the deck an inch or so in front of it, so maybe it had some form of linkage that allowed it to be adjusted from outside the hull.
I think I'll leave the colour as it is, just tidy it up a little, replace a few of the missing fittings etc, pop a little brushless motor in, add the radio gear and enjoy it the way the builder wanted it to look...