A run of tough games ended with a third consecutive London 1N defeat for Diss despite a spirited show at third placed Letchworth.
Phil Sharpe's side were only 10-8 down at the break but were unable to keep pace with a strong home side after the interval.
Diss had the consolation of crossing the Letchworth line twice, with Warren Wilby and John Laurie scoring the tries. One of the scores was converted by Chris Beaird who also notched a penalty.
'There was no flow to the game and the referee didn't help, showing six yellow cards, four to them and two to us,' said Sharpe. 'Having said that Letchworth were the better team and deserved to win. Everyone seems to be doing their job well individually but for some reason we just don't seem to be clicking as a team at the moment. When we do then I'm sure the wins will come.'
Diss play Ruislip at home next.
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