IPP_Questions

I was part of a International Pension Plan (IPP) for a few years though my then employer it was a post A day (2006) plan which I contributed to for circa 5 years. This is a Guernsey based pension scheme. I stopped contributing to this scheme and have since decided that I want to be permanently domicile in the UK. I also part of a UK registered pension where I have been contributing. However I have to date not been able to understand how I can access my IPP funds at 55 or how/if this would affect my LTA and tax free portion. I ideally would like to transfer the entire international pension into my UK pension or just pay the tax and bring the fund. Is there a help desk at HMRC where such queries can me made? I am not looking for tax advise just want to understand the rules and when I speak to the provider and their advsiors I get nuanced answers. Can anyone help?