Another issue which is specific to Swanwick is that of electronic coordination.
With flights such as yours which climb in Swanwick's airspace, the initial sector(s) have to make a judgement of what is your requested (not always the same as filed) level (if you're not yet on frequency), what level you might make by the relevant sector boundary, what level might get accepted by the next sector considering their traffic, and any standing agreement issues. What generally happens is we will take a punt on that decision and offer electronically (to LMS in this case) a certain level. The time parameter for that offer to the next sector is set by the computer and we must get a level put in before the computer makes one up! The tactical controller (the one you talk to) will then see that level on his screen and climb you to it as his own traffic allows. It may well be (as in this case) that the next sector has conflicting traffic and will offer back a revised level for acceptance (280 in your case). This will be because of their assessment of where you fit in with THEIR traffic (it seems from your description that to accept you at 290 would have been a BAD idea!). You will then get the "At the request of the next sector..." speech. What we always hope is that the amended offer will come back BEFORE you have passed that level. Unfortunately that is not always so, so the roller coaster starts.
In summary, then, we all try to plan ahead as far as possible, but we are limited by the time constraints of the electronic data interchange and the tactical situation may be slightly different to the initial planned one.