Labour faced stinging claims yesterday that shadow chancellor Ed Balls’s commitment to cuts makes the Conservatives the party’s most natural coalition partner.

Plaid Cymru MP Jonathan Edwards accused Labour of planning to spend less than Thatcher in government, leaving Britain’s biggest parties hard to tell apart.

But Labour insisted voting for smaller parties like Plaid at May’s general election would make five more years of Tory rule more likely.

The row erupted as Mr Balls set out Labour’s alternative to Chancellor George Osborne’s plans to shrink state spending to 1930s levels.

Mr Balls said the Tories’ “extreme and ideological approach” goes far beyond deficit reduction but repeated his warning that “Labour will need to cut public spending in the next parliament to balance the books.”

Seizing on the statement, Plaid’s treasury spokesman said: “Labour might talk the talk about offering an alternative to the Tories but the reality is that both parties’ spending plans are just two sides of the same coin.

“Ed Miliband and his party will in fact spend far less on public services as a proportion of UK wealth than Thatcher if they’re in power after May.

“The most natural coalition in Westminster based on the respective spending plans of the parties is a Tory-Labour partnership.”

Mr Edwards’s attack fired the starting gun on a furious four months of campaigning in his Carmarthen East and Dinefwr constituency.

Labour needs a swing of 4.6 per cent to claim the west Wales seat, which is number 66 on its target list.

And Labour candidate Callum Higgins yesterday issued a sharp rebuke to the Plaid MP, calling his comments “an embarrassing attempt at electioneering to gain exposure for their narrow nationalist agenda.”

He said: “Labour will never enter coalition with the Tories, the very suggestion is ridiculous, as well Mr Edwards knows.

“Plaid, on the other hand, came very close to entering a formal coalition with the Tories in the last assembly and just last year (leader) Leanne Wood said that she’d ‘work with any party … that includes the Tories,’ when questioned about potential coalitions.”