The product referred to was almost certainly Mather's Black Beer. Up until 2012, although it had a hell of a kick at 8.5% ABV, it wasn't officially classed as a 'beer' as far as the tax system was concerned. So there was no excise duty charged on it.
However that changed in the 2012 budget, doubling the price of the product:
https://www.theguardian.com/business/2012/apr/05/black-beer-future-budget-tax-relief
As predicted in that article, the manufacturer's were soon forced to cease production, as confirmed by their press release here:
http://www.continental-wine.co.uk/News.shtml
Mather's Black Beer was actually a 'spruce beer'
https://en.wikipedia.org/wiki/Spruce_beer
but, unless you can get hold of specialist beers brewed in the USA and New Zealand, it's no longer commercially available.
If you know a home brewer though (who has got access to plenty of spruce needles) there are several recipes on the web.