A senior Labour MP has refused to comment on a forgery row involving fake letters about him being sent to a local newspaper.

Former defence minister Adam Ingram is not responding to questions about how a 75-year-old Labour member's name was used to defend the MP's record in a series of letters. Councillor Michael McCann, the MP's aide, also declined an invitation to discuss the subject on Ingram's behalf.

Ingram, who represents East Kilbride, Strathaven & Lesmahagow, was criticised recently for having the largest-declared outside earnings of any Scottish MP. The long-serving politician makes up to £170,000 in consultancies and non-executive directorships on top of his £63,291 salary. The revelation was followed by two letters being published in the East Kilbride News under the name "Tony Carlin", a former Labour councillor and party member.

One of the letters challenged the criticisms of Ingram's outside earnings: "Adam Ingram has served our town as both an elected councillor and as a member of parliament with distinction. He has fought for people across the constituency and has delivered for them."

It praised him as a "tireless campaigner" and noted his "indefatigability". The letter also attacked the local Green Party for its criticisms of Ingram's extra-parliamentary jobs: "The Green Party are against the redevelopment of the town centre, in fact, they are against any development in the town, full stop."

Another letter, again from "Tony Carlin", hit out at criticisms of the first piece of correspondence. However, the East Kilbride News has since reported that the two letters are forgeries.

Adeline Pandolfino, Carlin's daughter, told the newspaper that her father had neither authored the letters nor given his permission for his name to be used. She added that, if individuals did not want to put their own name on letters, they should "remain anonymous".

The typed letters had a superimposed signature at the bottom. The Sunday Herald left a message for Ingram and emailed him questions, but the MP declined to respond. Councillor McCann was also given the opportunity to comment, by email and through calls to his home and mobile, but he too did not get in touch.

However, both Ingram and McCann have commented on the outside-earnings row in the local press.

In a letter to the East Kilbride News, McCann responded to Green Party criticism of Ingram by stating: "Kirsten Robb, Green Party activist opposes the South Lanarkshire Local Plan and she opposes the redevelopment of the town centre."

Ingram, in a separate publication, defended his five other jobs: "The companies I am associated with came to me and suggested that because of my background, knowledge and experience, that I may be of assistance to them."

McCann is expected to be the next Labour candidate in the constituency, if Ingram opts against seeking another term. Carlin declined to comment. Pandolfino said she intervened in order to clear her father's name.

John Wilson, an SNP MSP for Central Scotland, said: "Given his position, Adam Ingram should make clear what his view is on this serious matter."

Robb said: "These bogus letters are disgraceful. Adam Ingram should answer questions."