You are correct. If I have tried to drive away and the trans judders/slips, knocking the gear shift lever into "2" allows the car to kick down into first gear and pull away OK.
When I put the gear shift lever back into "D", the 'box goes into second gear with no problems.
The most plausible explanation that I have had, is that the take up bands are tightening then slackening then tightening then slacking etc etc until it eventually picks up drive cleanly.
Thanks for the very prompt reply.
[This message has been edited by AidanSwords (edited 04-07-2000).]