Christians have damaged their ability to evangelise by allowing their faith to be defined by right-wing issues such as abortion and same-sex marriage, a leading member of the Scottish Parliament has warned.

"We have lost the initiative and allowed Christianity to be type-cast by right-wing ethical issues such as abortion and gay marriage," said Dave Thompson, the Scottish Parliament representative for Skye, Lochaber and Badenoch.

Christian politicians were "pressurised" into either being "very quiet" or "hiding" their faith altogether, Thompson told Christian Today in the build up to a debate at the Edinburgh Fringe Festival yesterday.

Christians have allowed their faith to be stereotyped as solely being concerned with right-wing ethical issues because of an unwillingness to share their faith, he added. "I would say that a lot of this we've bought on ourselves in the sense that we've been too quiet about what Christianity is about and we've allowed ourselves to be defined on would be regarded as ring-wing issues such as abortion."

The MSP is part of the left-wing Scottish National Party and holds traditional evangelical views on abortion and same-sex marriage.

"I'm against abortion," he said. "I've always been against abortion except in exceptional abortion like when a mother's life is in danger."

He added: "I thought same-sex marriage was a step too far...so I voted against it when it came up in the Scottish parliament."

However he said he resented that this was what shaped public perception of Christianity. "Those [issues] are important but Christianity is not just about that," he explained.

Thompson called on politicians and people across society to be more open about their faith. If they did that, "maybe people would think to themselves there is something in this but if we don't tell them, how are they meant to know?"

He described his own faith and how more politicians should be prepared to discuss their faith. "My faith is something that shapes and defines me. The honourable thing to do for any politician is to let their constituents know what shapes them."

"You have to be ready for people to have a go at you and categorise you as a bigoted person etc," he admitted when asked about attacks on Christian politicians.

Thompson also believes there has been pressure on politicians in recent years to downplay their faith or hide it altogether.

"I don't think it can be a private affair," he said. "There is no way you can separate your Christianity from your daily activity. It is a part of you; an essential part of you. Politicians should be upfront about that and people can make their own judgementss"