How to / is it possible to straighten a bent seatstay/chainstay on a steel frame? At home or inexpensively by a professional I have a Genesis Croix de Fer 20 (725 Chromoly) and crashed with my friend on his bike. On one side the back of the frame bent out so the wheel drops out, it is bent but not crumpled. 

I would like to know about the options for fixing it either myself or by a pro without costing too much (I think I could get a new frameset for £350). I am based in Denmark

any help much appreciated I have attached a picture of the fram.

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Rear triangle rear alignment of a steel frame is well within the scope of a home mechanic. There are professional tools available but functional versions can be made cheaply from lumber and generic hardware.

RJ the Bike Guy has some good videos on his YouTube channel (embedded below) that show how to measure how far the stays are out of alignment, how to re-align them and how to re-align the dropouts 

You will of course have to make a determination as to whether your frame is too deformed to be safely re-aligned. Once you have determined how far the stays are out of alignment you can seek advice and make that decision.