A Labour MP warned the Government yesterday of his fears over the risks to service personnel who have been exposed to depleted uranium.

  The concern was voiced despite assurances by Geoff Hoon, the Secretary of State for Defence, at question time. He said: "In the absence of any specific evidence whatsoever to link DU with any particular illness the reality is it is extraordinarily difficult for any government to prove a negative".

  Fresh medical tests into the health effects of depleted uranium shells were announced last Tuesday.

  But, during a series of exchanges, John McFall, the Labour MP for Dumbarton, said: "Given that the ministry was warned 10 years ago on this issue... is it not the fact now the burden of proof should be on the ministry and other Government rather than on individuals who are ill having to prove that their illness is a direct result of this DU?"

  Dafydd Wigley, the Plaid Cymru MP for Caernarfon, went even further in his attacks and claimed there had been a "cover up" by the Government because previous parliamentary answers had provided "misleading" information about the issue.

  Earlier, the Government was accused by the Tories of being divided over its support for the so-called Son of Star Wars, the American missile defence system, because of some ministers' links to the Campaign for Nuclear Disarmament (CND).

  Iain Duncan Smith, the shadow Defence Secretary, sought to reignite the argument over the defence plan, which has the support of President-elect George Bush, and the new American administration.

  Mr Duncan Smith told Mr Hoon: "You know that the MoD is advising you that there is a growing threat. Doesn't that explain why in the last year and a half, you and your colleagues have been going to Washington and letting them know, privately, you would be willing to upgrade Fylingdales, providing they did not ask that question before the next election?

  "If that is your private view, why has the [Foreign Office] Minister of State [Peter Hain] said in March last year, 'I don't like the idea of a Star Wars programme, limited or unlimited'.

  "Isn't that the public face of the Government's position, although privately they are pretending something else? The Government resembles more and more, Dr Doolittle's Push-me-Pull-you – hoping that something will turn up before the election."

  Mr Hoon said: "The Government have not yet reached a decision on this matter – nor should they do so because the Americans have not reached a decision. In the light of a new US administration, it hardly seems sensible to commit ourselves to something that the Americans may or may not decide to commit themselves to."

  He said that after security reviews, the Government "apprehend no immediate threat to the UK from so-called rogue states or the proliferation of nuclear weapons. It is obviously a matter we have careful regard to. But it is a matter that is equally under careful consideration in the US."