The Government Gateway was the system used to sign up for the UK government’s online services. It got shut down in March 2019.
Log in to HMRC’s replacement system, HMRC Online Services.
Yes, but only for HMRC Online Services.
If you don’t remember your sign in details, here is how you can find your Government Gateway user ID.
You can also reset your old user ID and password. Though, we are unsure how long you will be able to do this for.
Instead, we recommend you sign up for the HMRC Online Services or sign up for GOV.UK Verify.
It all depends on which service you need: DVLA, Department of Agriculture, etc.
Here is the official full list of alternatives.