For mental gymnastics like this, I turn to this website:
http://www.measuringworth.com/index.php
I come up with a current sterling conversion of 200,000 yen in 1972 of about £2,700 in 2011.
Here's how I get there:
US$1 = 303 yen and US$1 = 40 pence in 1972.
Therefore, £1 = 758 yen and 200,000 yen = £264 in 1972.
The inflation factor since 1972 in the UK is approximately 10.3. That is £100 today buys what £9.71 did back then.
£264 X 10.3 = £2,719 in 2011 currency.
However, that's based on your example being a new watch in 2011, which it is not. The question we need to ask is what would a used JLC that originally sold for £2,700 now be worth? Watches are a lot like cars, in that they lose a good portion of their value when they go out the door of the dealer, So I'd say maybe half that figure at retail, less on eBay or at auction.
IMO the £1,400 figure is probably too high and £350 is way too low,
gatorcpa