The driver of the bus was allegedly told the mobile clinic would not be welcome in the Markets area of south Belfast because Mr McCartney’s sister Gemma, who is a nurse, was part of the crew.

DUP MP Sammy Wilson yesterday told the Assembly that a member of Sinn Fein was involved in the incident.

Sinn Fein’s Alex Maskey responded angrily to the allegations.

The South Belfast MLA said: “To set the record straight there was no member of Sinn Fein involved in any way, shape or form in any incident involving this cancer bus.

“It is disgraceful that anyone should seek to exploit this valuable community service to score cheap political points.”

DUP MLA for the area Jimmy Spratt and party health spokeswoman Iris Robinson met with senior PSNI officers in the area yesterday to discuss the issue. Mr Spratt said senior police officers reassured him they would be fully investigating the incident.

“The driver of the bus was told in an intimidating way that they were not welcome in the area because of the presence of Gemma McCartney,” he said.

“So far no official complaint has been made but the police have assured me that they will be in contact with Gemma McCartney and other people involved.

“We were concerned that there may have been political pressure brought to bear to stabilise the political process, but they have assured us that they will carry out any probe regardless of any consequences.

“It was a very positive meeting and we were reassured it would be properly dealt with.”

He said people who were being intimidated needed to come forward.

Mr Spratt said the incident could have serious repercussions: “The alleged involvement of a community leader, with close ties to Sinn Fein, raises questions over the support for law and order amongst some republicans in the Markets area.

“The McCartney family has suffered enough and certainly should not be subjected to intimidation like this.”

Mrs Robinson said: “The fight against cervical cancer in Northern Ireland is far too important an issue to be put at risk by the thuggish behaviour of some self-appointed community representative.

“The health of the Markets’ women should not be placed at risk in this way.”

The PSNI said it would not comment on the incident or the security of individuals.

“We never ignore anything that would put someone at risk and where we receive a report of a threat or threatening behaviour, a full investigation is carried out.”