If your local Post Office has closed down, have you considered having your items collected from you by the Post Office? If you type Royal Mail Collection Service into Google and run a search on the term then you should see something in the results resembling the first of the two screenshots that I have included below.
Once you see that option in the search results click on the line that begins "We can collect your parcels..." and a second page will load up, showing the second screenshot included in this reply. Therefore, if you are unable to get to your nearest Post Office now that the one that you used to use has closed down it may be easier to make use of Royal Mail's collection service so that they come to you and collect the item(s) that you want to post, rather than you having to make an eight mile round trip to go to what is now your nearest branch.
First Screenshot Shown Below:
Second Screenshot Shown Below:
