He works mainly at Cosham Park House and his specialism is in paediatric medicine.
http://www.portsdowngrouppractice.co.uk/about...

Complex healthcare procedures have better results if they're performed by individuals who do that procedure regularly,” says Dr Rosser, who is UHB's medical director.
He looked at the UHB areas of specialism, such as renal, knee and plastic surgery, that treated at least one military patient between 2005 and the first half of 2008.

auch "specialist field"