i have a plug in electric radiator(which is in good condition but an old style) would you think that this could be used when and if neccessary in my two bay hobby tunnel.
A heater of this size is likely to be too small for a two-bay hobby tunnel. It would suit an 8 x 12 feet greenhouse, but might address relatively minor levels of freezing weather in a somewhat bigger space.
There is an issue about the suitability of a heater designed for indoor use in a polytunnel as it may not be adequately insulated for a damp environment. It would be wise to consult with a qualified electrician about the heater and its installation.
At the very least a suitable RCD circuit-breaker should be fitted to protect against electric shock.