I think there have been reports of Orange holding IPP artificially low when exchange went 21CN. You need to phone them but whether they understand IPPs is anybody's guess.
Is the "up to 20Meg" upgrade automatic, or do we need to phone them up
No, you have to take out a new contract.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC