Part of the problem is its only worth what someone is willing to pay, and that in turn depends on what they want it for. They don't come up for sale very often and those that do vary enormously. Any running rigid/girder has to be worth £3500 / £4000. Being an army bike probably adds a £1000. But then theres the question of originality vs restoration. Some people like their bikes to look factory fresh but I'd suggest military enthusiasts tend to lean towards the untouched look. Unless of course you want to do film work. And then there is provenance, if you can show it still has its proper service paint & correct contract number and, better still evidence that it would have seen service you can add on more. On the other hand no-one expects them to have matching numbers, in fact Id be a bit suspicious of one that did.
I'd say 9k and see what they say. Always good to start high