Unfortunately my rear tyre has a small brass nail in it i'm unsure of the size so i've just left it in as theres no problems with leakage i don't see the point in fixing it as i'll be getting some new tyres soon.
What you are riding about with a nail in your tyre?
My policy if I find anything in my tyre, is to ride slow as foc till I get home or somewhere convenient to pull it out. Then surprise surprise I pull it out. If it's shallow tack and it hasn't punctured the tyre - well magic. If the tyre goes down, well it's time for a proper repair or a new tyre.
Never ever ever ride about with a nail, screw, tack or whatever in your tyre. If it works loose you then have a deflating tyre, or worse if it comes right out you can have instant total deflation.
I once had my tyre punctured at speed on a dual carriageway, something punched a hole in it, it went down in seconds. I probably only managed to stay on the bike as I was on a straight bit of road at the time, and lucky for me near an exit (so lucky again I didn't have to sit on the hard shoulder waiting for recovery). The tyre was totally focced and looked like it was trying to work it's way off the rim.
Attend to debris in your tyres in a timely manner.
Nail in tyre, surely to god is a fail, and they should be advising you not to ride it.