NORTHERN Ireland First Minister Ian Paisley Senior came under increasing pressure to quit politics this week after the dramatic resignation of his son as a junior minister.On Monday Ian Paisley Junior resigned as a minister in the Stormont Assembly over increased public criticism that he had improperly lobbied government ministers on behalf of business associate Seymour Sweeney.In April last year it was revealed that Paisley Junior had lobbied government ministers and senior civil servants to support Sweeney's plans to take over Northern Ireland's top tourist attraction, the Giant's Causeway.While Paisley Junior initially claimed to have had minimal contact with Sweeney, it later emerged that he had not only gone on fishing trips with the developer but had also bought a house from him.Paisley Junior insisted that he had done nothing wrong in lobbying government ministers on behalf of the businessman, and insisted his decision to stand down as a junior minister had not been forced by the criticism of his relationship with the property tycoon."The past 10 months have not been without controversy," he said. "Personal criticism, unfounded allegations, innuendo and attacks on me personally, followed by Ombudsman's reports that have cleared me - this relentless period of criticism by those who have decided on this path has been unceasing."The criticism has been a distraction and has got in the way of the activities of this government and importantly it has gotten in the way of the activities of my political party."Nevertheless, Paisley Junior's decision to stand down as minister has increased pressure for his father to also now leave Northern Ireland politics.Paisley Senior's decision to go into government with Sinn Fein last May has led to severe criticism from hardline Unionists within his own party.He has already been forced to stand down as leader of the Free Presbyterian Church, which he personally founded and led for the last 50 years.It is now speculated that Paisley Senior may decide to stand down as First Minister following a special U.S. business conference to be held in Belfast in May.Northern Ireland Secretary Shaun Woodward admitted that this week's resignation was upsetting for the Paisley family."On the public front it is obviously a matter for the Democratic Unionist Party and obviously a matter for the Executive and Assembly," he said."But on a private front I think one also has to acknowledge that, for the Paisley family, it is a very difficult time. These matters are always very, very hard and for them, a family who has given a huge amount to Northern Ireland, my thoughts are also with them."SDLP assembly member Declan O'Loan described Paisley Junior's resignation as "inevitable," but admitted it now called into question the future of his father."It is clear that within his party the embarrassment has become too great and he had to go," he said."The spotlight now switches on to Ian Paisley Senior. I think the public will be saying one Paisley has gone, when is the other going to go?"