Getting it wrong, twice

Sectarianism is a problem in parts of Scotland, Rangers and Celtic being the prime example of two competing factions vying through the tribal fan system of football to make their mark over a hated rival. It isn't racism as you'd be very hard put to tell the difference between the supporters without their colours, it isn't religious either, though a difference in religion goes deep within the two communities.
It's not something we're used too in England, the religious aspect anyway, though the tribal rivalries of football fans we're well used too. However what we wouldn't do, is call for a football clubs fans to not fly a flag that represents their country, after all, that would be a bit racist, wouldn't it?
Mail.

For almost 130 years the proud supporters of Berwick Rangers have revelled in the fact that they are a British team playing in the Scottish Football League.

Ok, lets get the sodding obvious bit out of the way first, whilst Berwick Rangers are a British club, so are the rest of the teams playing in the Scottish Football League! Berwick are different only in the fact that they are based in England!

They call themselves The Borderers, and proudly display both the St Andrew's cross and the St George's cross on their scarves and merchandise.
But now the club's supporters have been told that they can't show the St George's cross when attending away games - because it incites sectarian tension.

As sectarian implies religion, I cannot see how flying a flag of St George is being sectarian, what it does imply that this club is English and that it's not sectarianism we're talking about here, but racism. They aren't particularly protestant, they certainly aren't Scottish (much as many Scots would claim)
Personally I think it's rank hypocrisy of Stranraer FC to claim sectarianism, when the plain facts speak for themselves, they are indulging in racism. However by calling it sectarianism they hope to get away with it, save only that the idiots at the Daily Mail decided to do an article on it.