Yes and no.
To work in the UK as a doctor, you must have GMC registration. Passing FRCPath part 1 will not grant you that. The best place to find out whether you need registration and which route is the GMC.
Take this test: https://www.gmc-uk.org/registration-and-licensing/join-our-registers/registration-applications/application-registration
Typically, as an overseas microbiologist, you will need either the PLAB route, full FRCPath or sponsorship/MTI.
Once you have GMC registration or are eligible for it, you need to find a job and send your application. Jobs can be found in NHS jobs, Trac jobs, or BMJ. You can also find jobs via recruitment agencies, but ensure you find a reliable one. Once you have applied, you will go through a shortlisting process. This is where your Part 1 FRCPath will be useful, as you will get an advantage over those who do not have the FRCPath Part 1. If shortlisted, you will have an interview. Microregistrar has a WhatsApp group where you can ask questions if you have any. You can ask to join this group via our Facebook group.
Will working in the UK or a clinical observership improve my chances of passing the examination?
Certainly, you will know our common problems and how we manage them. This knowledge is invaluable. However, you must balance this advantage with the expense and difficulty of getting such a post.
I know many candidates who passed the exam without working in the UK. You have to be thorough and diligent. In my experience, being active in the forums (WhatsApp, Facebook) is important. Ask questions, and clear your doubts. Making a mistake in the forum is much better than making it in the exam.