start looking through your loose change.undated 20 pence coins are circulating.ebay are selling them. one is £130 at the moment.check out these sites. good luck.200.000 in circulation
https://shop.ebay.co.uk/?_from=R40&_trksid=p3907.m38.l1313&_nkw=20+pence+coin&_sacat=See-All-Categories...