More than half a million Scots are either not working or under-employed, union leaders have estimated.

The Scottish Trades Union Congress said it believed there are some 502,655 people who are under-employed or are out of work and want a full-time job.

It said this full-time employment deficit was much higher than the unemployment rate of 8.5%.

STUC general-secretary Grahame Smith said: "The figure of 502,655, a rate of 18.6%, is stunning and should cause government at all levels to pause and reflect.

"There are simply far too many people in Scotland at this time unable to access the quality, full-time work opportunities necessary to provide for a decent standard of living for themselves and their families."

The STUC estimated there are 167,170 who are unemployed and want a full-time job, along with 133,555 people who are classed as being economically inactive — meaning they are out of work but do not meet the internationally agreed definition of unemployment — and who are also looking for a full-time position.

A further 201,930 people are estimated to be under-employed, such as those people who are in work but want another job with more hours.

Mr Smith said the figures were a "robust and conservative" representation of the situation.

He stated: "Despite the rapid increase in Scottish unemployment at the end of last year, the STUC remains frustrated by the complacency of many politicians and policymakers on the current state of the labour market. The focus only on headline figures serves to obscure some of the most worrying labour market trends.

"Consequently, the STUC developed this new estimate which counts those people currently identified as being ILO unemployed, those who are inactive but recorded as wanting a job and those currently identified as 'under-employed'.

"In making the calculation we are careful to adjust figures to account for recent changes in the labour market and the number of unemployed people is adjusted to match the proportion of full-time jobs in the economy. The STUC is convinced that this is a robust and conservative estimate."

A Scottish Government spokeswoman said it was "using all levers currently available to us to stimulate growth and job creation".

She said: "We still have a situation of higher employment in Scotland compared to the UK as a whole, lower economic inactivity rates, and a lower unemployment rate compared to most of the other nations and regions of the UK, but we are clear that more needs to be done.

"That is why we are calling on the UK Government to take real action to strengthen recovery, and for a UK-wide jobs summit to agree an immediate programme of employment creation.

"Only with access to all the levers of economic growth can we maximise Scotland's potential to secure new investment and jobs, and that is why we will publish our consultation document next week for people to discuss the arrangements for Scotland's referendum."