KiwiGf, not the only culprit but needed if you want that white head on it . Even the bottled original stuff is pasturised now where as you used to be able to use the yeast in the bottles to brew stout.
Well I didn’t know cans and bottles are probably pasturised, but for me real ale is sold draft and comes from a barrel. I have only once found a British draft real ale on sale in a NZ, and that was by “accident”, it was a scottish one being sold as the “special” beer in a Wellington pub, it had been flown in and had to be drunk within a couple of days. Which I helped with, despite the price of 8 quid a pint (in 2012).
There is british guy 15 mins ride away who has a mini brewery and a tiny pub to sell his beer, a couple of the beers brewed are more than ok, some others are chilled and more like NZ craft beers and made to suit local taste I guess! but despite that I am still looking forward to a trip to the UK to do some sampling, once that trip is possible (and safe).
https://www.regent58.co.nz/