I have the same setup as you. What type of option strategies are you trading?
IB won't let me trade any debit or credit call spreads on single equity options and not on almost all index options, the exception being SPX becasue it is US and European style exercise. I can't even do call spreads on the FTSE100 index options even though that is also European style exercise. Debit call spreads are limited risk but it seems that IB's system doesn't recognise this, and it's not allowed just because there is a blanket ban on selling calls irrespective of the fact that there is a long call covering the risk in a spread trade.
IB says that the only way they would allow these trades if the account was a margin account but a SIPP account from C&P pensions is cash only. Are you trading options strategies where none of them involve a short call leg?
Late comer to this thread. I'd be interested in any information in regards to this. I'm already successfully trading options via Interactive Brokers via a corporate account and would like to open a SIPP account as well. With my existing account it is a margin account so I trade what I like without trouble. Ideally I'd like the same flexibility with the SIPP account...