Sara
The FRC will be closing in 6 weeks, so you may be too late for that anyway! But since you want to look up Metropolitan Police and military records you would need to go to The National Archives at Kew for those.
There is a lot to take in at Kew, and some people can find it a bit overwhelming at the first visit, but you can do some homework in advance by getting to know and love the website and the online Catalogue before you get there.
www.nationalarchives.gov.ukFrom the homepage, follow the link 'visit us' to get the basics about opening hours, readers' tickets, how to get there etc. The other really useful links are the dropdown menus 'Research, Education and Online Exhibitions' which you can use to get to a list of nearly 300 research guides, and 'Search the Archives' that takes you to the Catalogue. If you are new to research you should look at 'Starting Your Research' also on the 'Research...etc' dropdown menu.
As you will also see from the website, there are a lot of alterations going on at the moment, and the seating capacity is reduced, but provided you get there early in the day you should be fine. You will need to have a Reader's Ticket if you want to look at original documents, but you can pre-register online, or wait until you get there. Just make sure you have the right ID with you when you go. There are plenty of staff to help you.
There are other places that you may want to visit, such as the Probate Registry, but it depends on where you ancestors came from, and their occupations. Since you are interested in the Met Police, I assume you have some London ancestry, so you will probably want to visit the London Metropolitan Archives, who hold records for MOST of what is now Greater London.
www.cityoflondon.gov.uk/Corporation/leisure_heritage/libraries_archives_museums_galleries/lma/lma.htmI hope you enjoy your visit, and have a successful time with your research. I'm off to Edinburgh and Glasgow next week on my annual research trip to do my own family history, which I always look forward to for weeks ahead.
Mean_genie