Ok, that sounds reasonable. I'll admit I don't know the process of moving your registration portfolio from one department to another. However, if your last lab closed or lost it's IBMS training accreditation then it looks like a valid reason to reuse the previous evidence.
As for the interview itself, I'd make sure you're clear on the following:
The logistics of the service: so the pathology services at CXH are run by North West London Pathology, so be aware of how that sits as a partnership with Imperial. Make sure you know the Values for both NWLP and Imperial and have an example of how you meet them. This is particularly important because it's easy to show that you want to a job that finishes your portfolio and aim for an HCPC registered post, make sure you have a good answer for why you want *this* job in *this* department. Something that shows you're committed for the longterm.
UKAS. That UKAS is the sole national accreditation body and verifies medical labs against the ISO:15189 standard. Have an idea of how you would help a lab prepare for the UKAS verification.
As it's biochem, I'd be particularly aware of the difference between Internal Quality Controls, Kit Controls and External Quality Assurance (UKNEQAS is the big one, but it would be good to show that you know that there is a biochem EQA scheme run out of CXH -
https://deqas.org/).
For a band 4 post, I'd expect to see questions that show understanding of Levy Jennings plots for IQC, and some of the Westgard Rules that are used for governance. Sometimes you can see questions on your understanding of Uncertainty of Measurement so I'd make sure you're aware of the impact on patient roles. As an AP role is supporting the technical laboratory work, make sure you can speak about what is within your scope of practice and when you would refer something to a senior colleague.
You want to make sure you're aware of the idea of using SOPs, why they are important and why it's essential that you never carry out a procedure without proper training.
Make sure you have examples of how you have demonstrated your ability to work as a team player, any leadership, communication skills. Since a band 4 will be incredibly competitive with other graduates - if you can then try and find ones from your last lab to demonstrate that you've learned from that work experience.
Considering you're worked on a lot of your portfolio, this should be things you've already got knowledge of.
Does this help?