Former Holyrood politicians, including an ex-Tory MSP and the leader of the Scottish Senior Citizens Unity Party, have spoken out about their support for independence.

Nick Johnston, who represented the Conservatives in the Scottish Parliament for just over two years, said leaving the UK would give Scotland the chance to "create a fairer, more equal society".

He joined former Labour MSP John McAllion, ex-Scottish Socialist Party (SSP) MSP Colin Fox, former Green MSP Shiona Baird and John Swinburne, who represented the Scottish Senior Citizens Unity Party.

The group spoke of their backing for independence 15 years to the day after the opening of the devolved Scottish Parliament.

Mr Johnston, who was an MSP for Mid Scotland and Fife, said: "It has become clear that as part of the UK we are being asked to take part in a society that is becoming more divisive. Only with independence will we have a chance to create a fairer, more equal society."

Mr McAllion, who was a Labour MP before switching to Holyrood, said: ''When I was at Westminster, I quickly realised it wouldn't deliver for Scotland so I went to the Scottish Parliament hoping it would be different. However, again here I soon discovered it didn't have enough powers to deal with social injustice.

"Devolution is not enough. It's very clear that under this settlement poverty is getting worse. The Scottish Parliament doesn't have enough powers."

Mr Fox, the current SSP co-convener, said: "How time flies. With the Scottish Parliament now 15 years old, the Scottish Socialist Party today joins with all our partners in Yes Scotland in hoping to see it assume all the powers of an 'adult' Parliament before its 16th birthday.

"In the Parliament's short 15-year existence, it has legislated to implement a smoking ban in public places, free bus travel for pensioners, free personal care for the elderly, abolished prescription charges and introduced equal marriage. But we can do so much more with the full powers of independence."

Ms Baird said: "When we started it was a new parliament and since then, term on term, we have been maturing. At this point we are in a good position to say we can go it alone and take our own decisions."

Mr Swinburne, who is still chair of the Scottish Senior Citizens Unity Party, said a Yes vote in September's referendum would be good for the elderly.

He argued that leaving the UK would allow Scotland to "change the value of our pension and the retirement age" and added: "We have seen time and time again that Westminster can't be trusted to look after our pensioners. We have been badly let down by successive UK governments, including Gordon Brown's pension funds tax raid and David Cameron's cuts."

Mr Swinburne said: "It is a scandal that in such a wealthy country as Scotland people, old and young, are suffering like this. We have to do something about this and giving the Scottish Parliament the powers that come with independence is the best way to go about it."

Dennis Canavan, chair of the pro-independence campaign Yes Scotland's advisory group, welcomed their remarks.

Mr Canavan, who served as a Labour MP and an independent MSP, said: "Over the past 15 years, the Scottish Parliament has had a good track record in delivering higher standards of social justice for the people of Scotland. For example, Scottish university students pay no tuition fees, Scottish senior citizens get a fairer care deal and we have a National Health Service in Scotland which is still freely available to all at the time of need.

"But the Scottish Parliament has limited powers. If the Scottish Parliament had all the powers of an independent parliament, it would be able to deliver so much more. For example, it would be able to stop wasting billions of pounds on nuclear weapons and also introduce a fairer welfare system, including the abolition of the bedroom tax, which would never have seen the light of day in an independent Scotland."