The Treasury chief secretary, Danny Alexander, one of the most senior Liberal Democrats, has said Britain's credit rating is not the "be-all and end-all".

The chancellor, George Osborne, has always put enormous store by the rating, issuing a statement on the eve of the Olympics opening ceremony to highlight how one credit agency had again reasserted Britain's coveted triple-A status.

Alexander's remarks probably represent the first time a government minister has downplayed the importance of the credit rating, but they reflect a wider view within his party that it needs to push harder for what it describes as a "Plan A plus" economic policy, in which greater emphasis is put on government investment, especially in housing, to boost demand and spending.

"The credit rating is not the be-all and end-all," Alexander said. "What matters is have we got the right policy mix for the country to get people back into work, to support economic growth, to deal with the huge problems in our public finances, and the credit agencies reflect on those things and the ratings they give are a reflection of the credibility of that mix."

It has been pointed out in some Lib Dem circles that the US lost its triple-A rating with some credit agencies before the summer but has not experienced a hike in interest rates.

Typically, a credit rating downgrade is seen as a threat to interest rates as markets take fright that a country will be unable to pay its debt.

Last Friday, Standards & Poor's said in a statement: "We project that despite recent weakness, the UK economy should begin to recover in the second half of 2012 and steadily strengthen, and we expect economic policy to continue focusing on closing the fiscal gap.

"In our view, monetary flexibility remains a key credit strength owing to the British pound sterling's role as a global reserve currency."

S&P said its stable outlook for the rating reflected its "expectation that the UK government will implement the bulk of its fiscal consolidation programme and that the economy should recover in the remainder of 2012 and strengthen thereafter".

But it added: "We could lower the ratings in particular if the pace and extent of fiscal consolidation slows beyond what we currently expect."

Dreadful growth figures released at the end of July showed the UK economy sliding deeper into recession, with a 0.7% fall in GDP between April and June.

After Osborne hailed the S&P judgment, David Cameron swung behind his chancellor, rejecting speculation that he may be shifted in a cabinet reshuffle and asserting that Osborne "is going nowhere". Labour responded by saying that if Osborne is going nowhere, neither is the British economy.

There have been reports that Osborne and Cameron are looking again at what measures can be taken to stimulate growth, including airport expansion. But UK growth prospects remain limited by the state of the eurozone economy. It is expected that growth will recover somewhat in the third quarter, partly off the back of the Olympics and the wider feelgood factor.