Yes, because Subway is the only place in the UK which sells pork.
Oh, wait...
Jews have been to the United Kingdom for the past 1,000 years or so. Pork is a taboo food for them too. Yet I don't see any of them demanding that restaurants should serve Kosher food and they should refrain from serving pork... just saying.
You don't think there are any kosher restaurants in the UK?
Also, there are close to a million Hindus in the UK, for whom beef is a taboo food. They are also not making any demands to ban restaurants which serve beef.
Who are making demand? From the link you posted, not Muslims:
This week people have taken to Twitter calling for a boycott of the chain, and protests have been organised for this weekend outside outlets nationwide.
But a spokeswoman for the company said the menu had not changed, and stores had been able to open as halal franchises since 2007, due to customer demand.
Turkey ham and turkey rashers are being used instead of pork products in 185 stores nationwide, where all meat is prepared according to halal rules.
Four stores in East Lancashire currently serve halal meat: Texaco Service Station in Nelson, Blackburn Beehive Service Station, the Blakey Moor store in Blackburn town centre, and Blackburn Total Garage.
In the past, police have had to intervene after right-wing groups organised protests outside KFC shops in East Lancashire when they started to serve halal meat.
[...]
A Subway spokeswoman for Subway said: “Due to the growing popularity of the Subway chain, with the diverse multicultural population across the UK and Ireland, we put a programme in place in 2007 to ensure that the population demographic is taken into account when new store openings are considered in order that we meet consumer demand in each location.
Subway thinks they can sell more sandwiches by allowing Halal franchises. That is the market at work.
From another link:
Both Stoke outlets are now serving halal-only products – the Shelton location since it opened five and a half years ago and the Tunstall store for the last few years.
They haven't suddenly 'banned' pork from 185 branches, there have been Halah branches for years, it is just that now someone has decided to publish a misleading story to stir up bigots.