What's the Name of That Book??? discussion

I read a book a long time ago and I can't get it out of my head! Problem is, I can't remember the author or title, only the start.

I remember there is a man (I'll call him P for reference) who deals cocaine to city traders, he picks up some tips by befriending these people and eventually becomes a city trader himself. A man introduces P to the firm that his father owns. P is very successful, and the other man's father almost sees him as 'the son he should have had' and is disappointed with his own son.

The father introduces P to a woman (and secret cabal?) who shows him how to perform astral projection. I think it's to other dimensions rather than time-travel.

I can't remember anything after this except that, while they are 'projecting', P asks her what their bodies are doing. She replies that they revert to a primitive state and sometimes end up fighting or having sex. When they return, P has a bleeding nose and she suggests that he tried to have sex with her while they were projecting and she punched him.

That's all I can remember but I'd greatly appreciate it if this rings any bells with anyone. I originally thought Margaret Atwood or Ian M. Banks but I don't think that's correct.

Thanks!

A long time ago, does that mean 2 years? 10 years? 30 years?

I found out from Reddit, FYI it is Transition by Ian M Banks.

Glad you found your book, John. Here's the link - Transition by Iain M. Banks.

Thanks