BBC Scotland's Chief Political Correspondent John Morrison reports

They may try, as has been alleged in the case of Kevin Reid, to set up meetings for their clients with those in power.

But they have come under fire on occasions and when the Scottish Parliament was being set up moves were made to limit the lobbyists' power.

In particular, Scotland's politicians were keen to prevent any repeat of controversies like the "cash for questions" row which have marred Westminster politics in recent years.

They decided not to give official recognition to lobby companies and to limit their access to the parliament.

Julia Clarke says lobbying is legitimate

But still the lobbyists can be found in the bars, cafes and restaurants of Edinburgh's Royal Mile where they seek the ear of the powerful to press their clients' case.

They seek to meet the politicians because they believe access can change policy.

Julia Clarke, of the Association of Scottish Public Affairs, believes the controversial business has its place when conducted in a reasonable manner.

"Lobbying is entirely legitimate in all its different forms," she said.

"You always do have to identify who you represent when you are in contact with the parliament, it's only fair.

"They have got to know where you are coming from, who you represent. You have to got be very honest and transparent in your dealings with them.

"You couldn't offer inappropriate hospitality. It's really common sense, it's about what the man in the street would think is reasonable."

Kevin Reid was filmed in secret before the allegations were made

The corridors of power in Scotland are easier to control than those of Westminster, according to some analysts.

But Joyce McMillan, who was on the Consultative Steering Group which helped establish Scottish Parliament procedures, believes that lobbyists may have limited power.

"Lobbying companies like Beattie Media only gain whatever value they are perceived to have from the perception that they are able to offer access to MSPs and ministers," she said.

"And if ministers and MSPs make it clear that they cannot offer that then really their market value is going to plummet."

After their employees were filmed allegedly offering improper access, Beattie Media said they had no influence over ministers.