Carlsberg is all about making money, primarily with Carlsberg lager. Their current marketing policy is to try sell as much stuff as possible at little margins.
Tetleys is on prime land, and was always going to be sold once the area around it developed and land prices increased.
Economics meant sense to sell up and move production elsewhere
Heineken did it closing Tyne Brewery, and then Dunston, so now ALL Newcastle Brown Ale sold worldwide is brewed at Tadcaster. It was cheaper to make it at Tadcaster, and tastes were the same, so it happened.
Kronenbourg, that traditional French premium lager is brewed at Tadcaster and Hartlepool!!!
Murphys, an alternative stout to Guinness is brewed at Tadcaster, as is Fosters and (ALL) John Smiths.
The big breweries are always looking to make money and cut costs. It's what happens in the big world. No loyalty to tradition. It's all about the 'brand' and marketing, and making as much beer as possible at minimum costs, and making a profit
For what it's worth, I hope you all boycott Tetleys and drink John Smiths
Personally I drink Bulmers, cos it's feckin cheap in the staff shop
Cheers
