HMRC have issued a press statement regarding the outage earlier today:
HMRC is carrying out some preparatory work as part of our plans to transition content from the HMRC website to GOV.UK.
Unfortunately visitors to the HMRC website were automatically redirected to GOV.UK for a short period earlier today.This problem has now been resolved and HMRC apologises to any customers who were inconvenienced over this short period.
The transition of HMRC content to GOV.UK will occur in phases over the coming months. We will announce further details of each phase of transition before we redirect customers to GOV.UK.
You can read more about our approach to transition in previous blog posts on this blog, how we are prioritising the topics that will be transitioned in each phase, and the work we are doing to build a new system for the HMRC manuals.