The Cardiff Blues and Gloucester are regarded as the biggest underachievers in Wales and England, but one of them will rid themselves of that tag at Twickenham next month. Whatever the result, it will be a bittersweet moment for the Welsh region's outside-half, Nicky Robinson.

The 27-year-old is leaving for Gloucester in the summer, with the Wales scrum-half Gareth Cooper moving the other way. Having been with the Blues from the region's inception in 2003, which followed the decline of Cardiff from inaugural Heineken Cup finalists to a club that made up the numbers in Europe, Robinson acknowledges that he is leaving at a time when the team has finally made it to the threshold of success.

"Leaving the Blues was a difficult decision to make," said Robinson. "I knew the team was moving forward but it was simply that I fancied a different experience. Playing in the final against Gloucester would not be a problem for me: winning a trophy would be the best way to mark the end of my time in Cardiff."

There is a precedent of sorts – the former Wales lock Steve Williams played for London Irish in their 2002 Powergen Cup final victory against Northampton, shortly after announcing he had signed for the Saints. "Nicky wants to leave us on a high and I know that money was not the reason he moved," said the Blues' head coach, David Young. "I can't see any problem in picking him for the final."

The Blues have won all 10 matches in the EDF Energy Cup and the Heineken Cup this season, a contrast to their indifferent form in the Magners League, and they prevailed in a tense encounter on Saturday evening despite having played only two matches in seven weeks and those without their Wales internationals, during the Six Nations.

"I was concerned we would run out of steam," said Young, who said he hoped the injured back-rowers Martyn Williams and Andy Powell would be fit for next month's Heineken Cup quarter-final against Toulouse, which is followed a week later by the EDF final. "We have come a long way in six years and it has been a bumpy ride. We face probably the two biggest games in our history next month but we know we are not the finished article."

Northampton have come a long way in a shorter time. A year ago they were playing in National League One and despite this loss they still have the chance of a passport to next season's Heineken Cup, through the European Challenge Cup.

The Blues held the ascendancy for long periods in a physical contest. The Wales wing Leigh Halfpenny was especially menacing but both sides struggled with the final pass and composure was lacking on an evening when only two kicks at goal, out of eight, were successful. It was a typical semi-final where the result counted for everything and for the large contingent of long-suffering Blues supporters it meant a return to Twickenham, a ground where, in their previous incarnation as Cardiff, their team used to play Harlequins every October until the inception of the English league towards the end of the 1980s. It was a fixture the Welsh club very rarely lost.

Cardiff Blues Blair; Halfpenny, Shanklin, Roberts, James; N Robinson, Spice; Jenkins, G Williams (R Thomas, 66), Filise (Yapp, 71), D Jones (Davies, 59), Tito (capt), Molitika, Sowden-Taylor, Rush (Morgan, 80).

Try Spice. Pens Blair 2.

Northampton Foden; Diggin, Ansbro, Downey, Reihana (capt); Myler (Everitt, 63), Dickson (Dickens, 73); Smith (Tonga'uiha, 50), Hartley, Murray, Fernandez Lobbe (Easter, 73), Kruger, Best, Gray (Lawes, 69), Wilson.

Try Ansbro.

Referee G Clancy (Ireland). Attendance 26,774.