I questioned it simply on the basis of numbers.
Whether 100K or 200K struck is immaterial. To have 700 of them is a ridiculously high number unless you have had access to a known pile of them.
Based on Wiki, which can't be accepted as gospel but should be of the correct order of magnitude, a total of 136m 2008 20p pieces were struck and the cumulative total of 20ps to that date was 3.248bn. 100K or 200K is only 0.07% or 0.14% of the total struck in 2008 and 0.003% or 0.006% of the total number of 20ps struck up to 2008.
Based on a random distribution, to acquire 700 would necessitate looking at 22,736,000 coins based on an average of 1 in 32480, or half these numbers if 200K were made. Nobody has that much time on their hands, nor would I say access to sufficient material in the normal course of events to find that many. I'm sure they were released into a specific area or two as part of a mint consignment, which could skew the distribution curve, but it is not realistic to find the numbers quoted just from a random search of your change. How many people would see even a couple thousand 20p pieces in their change over a 7 or 8 year period let alone more than 10 million.
To buy 700 off eBay or similar would cost too much, so ................ the whole thing just doesn't add up unless you were able to buy a mint bag of 20ps and they just happened to have a large number of no date coins. Or you can get them from alibaba.