I'm with Orange as it now is. It does happen but infrequently. Depends on many things - quality of your line, distance from telephone exchange, Orange themselves, how many other users in your area are connecting at the same time.
By the way Broadband is not dial-up but I suspect that to connect through the Speedtouch or Livebox you are treating it like dial-up.
If it gets bad contact Orange. Finding their phone numbers on their webiste is really difficult. It is article kb6571. The number you want is 08700102462 - at national rates.