The Westminster group leader of the Northern Ireland pro-British Democratic Unionist Party (DUP) has taken aim at the Conservative’s increasingly strident rhetoric over Scotland and the Scottish Nationalist Party (SNP), which they claim will damage the Union.

Writing for the Guardian newspaper Nigel Dodds, who leads the DUP party in Westminster, said the United Kingdom needs “responsible politicians”. Mr Dodds is the former MP for Belfast North, and is seeking re-election next week. The DUP are expected to win nine seats, the eight they already held plus East Belfast, lost by Alderman Peter Robinson in 2010.

Present electoral arithmetic suggests the Conservatives need the support of DUP MPs to deliver a viable minority government in the next parliament and Dodds’ response to Cameron’s comments on the SNP and English votes in parliament could cast doubt over the future of that arrangement. In the article, Dodds’ strongest criticism however was reserved for Nicola Sturgeon’s Nationalists.

He said: “Ironically the problem with the SNP will stem not from nationalist dogmatism, but almost unequalled political opportunism.

“A party that pledged itself at Westminster not to vote on non-Scottish issues, that swore the referendum was a once-in-a-generation opportunity and claimed Scotland was economically ready for separation, now reverses all these positions.

“It doesn’t matter that on any specific issue – say, full fiscal economy – SNP arguments disintegrate as soon as they hit reality, this is a party whose leaders will shamefully say anything in the expectation that their supporters will credulously go on backing them, whatever the flip flop”.

Turning his fire on the Conservatives, Dodds criticised present rhetoric questioning the legitimacy of SNP members voting on legislation in the Westminster parliament, which if applied universally would also de-legitimise his own Ulster MPs. Speaking of the idea there should be English-only votes for English laws, the so-called ‘EVEL’, Dodds said: “it’s not just a flawed political tactic, it’s also a constitutional mess.

“The Commons can’t be used as an ersatz, part-time English Assembly. It’s the union parliament, and abusing it in this way wouldn’t and couldn’t answer England’s real needs”.

The DUP did not historically support devolution, and were the only major party to oppose the creation of the Northern Ireland Assembly. However in recent years they have called for the creation of an English Parliament, to stabalise the Union and stop Scottish MPs becoming “second class” at Westminster.