Contact RIBA. It varies heavily.

If your degree is in visualisation and not architecture/designed based, unlikely you would get accepted to any Part 2 programme - but its all based on your portfolio and coursework.

Unis do accept non-architecture degrees but it is up to you to demonstrate your ability to work at that level - there isn't a 1st professional degree at master's level in the UK.  If your work is good enough you might be able to enter year 3 of the AA - then do 3 years for a part 1 - part 2.  Other part 1 programmes may offer advance standing but I have never heard of any offering more than 1 year of UG.

Contact RIBA, You may need to submit a portfolio to pass part 1 validation.

@Jamie Smith

Your best bet would be to contact the ARB (former ARCUK), as they are the statutory body regulating architecture in the United Kingdom.

There are more details on this page about the accreditation process, I think they might apply to your case - to summarise the main points, one is encouraged to check a list of RIBA-validated courses and make direct contact with course providers in order to assess one's options, and also to find more information on the website of the ARB.

You apply to ARB not RIBA to have receive Part 1 exemption.  RIBA has nothing to do with it.

ARB has a requirement that you must have an architectural degree to sit for Part 1.  You are much better off either getting into a Part 2 programme directly (again if your work demonstrates your degree had architectural design) then using your Part 2 portfolio to apply for a Part 1.  Else do the AA route which will be 3 years but you will have both Part 1 and Part 2.

Most UK Schools that offer 2 separate Part 1 and Part 2 awards have the option to offer you a place directly onto the Part 2 without a Part 1 - AA is a single award so different.

Top Unis such as Bartlett will not consider anyone onto the Part 2 unless they have a Part 1. But there are some 35 Universities in the UK that offer Part 2.