One needs to be careful with valuations for probate. Over valuing is only beneficial to the Inland Revenue and also can increase the expectations of the beneficiaries of the estate. An insurance valuation is for replacement by a machine of equivalent standard. The Market price of a machine will depend on the state of the market at that time and also how rushed one is to sell.
My advice would be to value the bike as if for a distressed sale. ie priced to sell within a month. This would then minimise the death duties payable and if you manage to get more once probate has been granted, then all well and good.
As usual the estimate of the bike’s value depends whether one wishes to buy or sell!
In the October copy of The Classic MotorCycle magazine there is a for sale advert with photo: “Scott Flying Squirrel, 1933, MoT May 07, taxed, well maintained and in pristine collector’s condition, full mechanical history, original logbook, £3500” and a contact telephone number so you could even check actual price received.
(Note: there is also another advert for a 1929 Scott which has had a “total rebuild'” (i.e. high price) but is unpriced – the price given is for the Royal Enfiled which is also for sale – but I would caution that there is a psychological step change from a 1930 and earlier machine (i.e. vintage) and 1931+ (post vintage) which impacts on price, plus the ‘total rebuild’ comment. Hence I would not recommend trying to use this one as a marker).
The 1933 one may give you a marker and, recognising Ian’s comment, this may need to be adjusted if yours does not reach this standard (e.g. not MoT’ed or taxed, not pristine collector’s condition). This, plus a suitable adjustment, may be sufficient for the solicitor preparing the probate if you are happy with this estimate.
If you cannot get hold of a copy of the advert, email me (you should get it from this web site, but if any problems my email address is inside Yowl’s cover as I am a club official) and I will scan a copy for you.