Thousands of gurkhas who have served with the British Army and want to settle here with their families will be allowed to apply for citizenship with PM Tony Blair announcing that immigration rules would be changed for them.Blair made the announcement yesterday after a lengthy campaign on behalf of the Nepalese soldiers. However, Gurkhas, who have served four years and were discharged after July 1,1997, will be eligible for ‘‘fast track’’ citizenship. They will be able to apply for automatic entry clearance either from Nepal or Britain on discharge. ‘‘I am pleased that so much progress has been made but I am very disappointed by the cut-off, which I think will be challenged,’’ Ann Wideecombe, the Tory MP from Maidstone, said.