John Simpson struck another career-best innings in a losing cause as Middlesex plunged to Twenty20 defeat against Somerset – their fifth in a row.

Simpson had plundered 75 in Middlesex’s recent loss to Gloucestershire and was the pick of the batsmen again with an unbeaten 84 from 51 balls at Uxbridge.

But it was not enough to halt his side’s losing streak in the T20 Blast as Jim Allenby slammed 89 not out and Somerset strode to a nine-wicket victory with two overs to spare.

Middlesex, who won the toss and opted to bat, got off to a lively start, with Paul Stirling (29) clubbing two sixes and two fours from the second over.

But Tim Groenewald (3-27) put the brakes on the home side, having ex-Somerset man Nick Compton (10) caught at mid-off and then persuading Stirling to attempt a cut that looped up to wicketkeeper Luke Ronchi.

Middlesex’s healthy scoring rate promptly ground to a halt, with England captain Eoin Morgan scratching around for seven before he was well held on the boundary by Peter Trego.

James Franklin (7) followed in similar fashion, holing out to long-off, and Andy Balbirnie (17) seemed to be finding his groove as he hit successive boundaries before top-edging a sweep into Trego’s hands.

Ryan Higgins (3) played on to Jamie Overton (2-44), as did Ollie Rayner (5) to Groenewald, and it was left to Simpson to steer Middlesex to a total of 171-7.

That always looked unlikely to be sufficient, particularly once Somerset openers Allenby and Johann Myburgh climbed into the home attack, bringing up 50 inside the first five overs.

Allenby reached his half-century from 25 balls and outscored his partner, who was put down by Higgins on the boundary when he had made 35.

There were some comic moments in one James Harris over, as Allenby’s top edge fell between Morgan and the bowler and Myburgh skied the next delivery, which dropped to safety as four fielders converged on it.

Myburgh (53) was eventually bowled by Franklin to end the partnership at 118, but it made little difference as Trego hit an unbeaten 28 from 12 balls, finishing with a huge six off Stirling’s long hop