A soldier who is considered too fat to serve his country can legally challenge a decision not to allow him extend his military service, the High Court has ruled.

As well as challenging the decision of the Minister for Defence to discharge him from the Permanent Defence Forces next month, Private Denis Dowd will seek a declaration that a Medical Corps Instruction, insofar as it refers to obesity, is repugnant to the Constitution.

Michael Howard SC, counsel for Private Dowd, told Ms Justice Mary Faherty in the High Court, that Private Dowd’s body mass index (BMI) is considered too high to allow him continue serve in the Army despite the fact that he is a keen sportsman and runs marathons and 10km races.

Mr Howard said Private Dowd had undergone a medical assessment which deemed his BMI so high it would prevent him obtaining a required medical classification to allow him extend his service in the military.

The court heard that despite having undergone a strenuous programme to reduce his BMI he had been informed by his commanding officer he would not be recommending an extension of service because of his medical classification. An appeal against the decision was disallowed.

Mr Howard, who was instructed by Private Dowd’s solicitors O’Regan Little, told Ms Justice Faherty that the method of assessing BMI used by the Defence Forces was crude.

He said other more accurate body fat indicators, including a skin-fold caliper test, should have been carried out.

He said that if such a test had been applied it would have resulted in Private Dowd being given a medical classification that would have resulted in his service being extended. A doctor who had assessed him said that he was sufficiently physically fit to be given a medical classification allowing his service to be extended.

Mr Howard said could run 10km in under 50 minutes and does it three times a week. He had completed five marathons, plays rugby with his local club and does circuit training twice a week. He had represented the Defence Forces in handball and soccer.

Private Dowd is seeking to quash the decision to discharge him and overturn the decision not to recommend him for extension of service. He wants a declaration that in assessing his health and suitability to remain in the Defence Forces on the basis of his BMI the respondents had acted unlawfully, unfairly and unreasonably and contrary to provisions of the Defence Acts 1954 to 2007.

Ms Justice Faherty granted him leave to seek a judicial review of his situation and placed a temporary stay on his discharge from the Defence Forces. The matter was put back until mid-November.