It looks like I've got a slow puncture, I've checked the tyre and can't see anything like nails, glass, holes etc. If I don't fix it, I can't ride tomorrow, do I need a new tyre?                                                                                                                                                                              

Has your tyre got an innertube? my tyre kept going down slowly over time, I got a 'puncture' on my way to the Farmyard, turned out the valve was broken, had to have a new innnertube, the tyre was fine.
                                                                                                                                                                             

If you really can't find the puncture (nails and screws are good at plugging the hole they created and can get worn down quickly...) then I suspect the valve - on tubeless tyres the valve is totally separate but should always be replaced at the same time as the tyre since the valve is subject to massive forces and wears out just like the tyre, but not all garages bother to replace the valve....

If you know a good garage or mechanic that will remove the tyre and plug any puncture with a professional repair then that should cost maybe £30 and will save the tyre

However the chances of finding that on a Sunday...?? er.....

Other option, for your run tomorrow, just pack a foot pump and top the tyre up occasionally   All depends on your appetite for risk though.....
                                                                                                                                                                             

My life is always risky, I do a Rick assessment every day lol                                                                                                                                                                              

How old is the tyre? how much tread is left on it? when you can get it to a tyre place if they find it is punctured and the hole is in the vicinity of the tyre wall they will not repair it. As has been suggested before, it could quite well be just a faulty valve, in which case, a very easy fix. As and when you have new tyres fitted, insist on new valves everytime, normally you wont be charged for the new valve, but if they do, it is worth a little extra for the peace of mind.

66                                                                                                                                                                             

The tyre is about 10 months old, tread is good, I will have a look at the valve, thanks 66.                                                                                                                                                                              

If you can get hold of a pair of high pressure valve caps  there made of metal and have an O-Ring seal in them it will get you round a leaking valve short term untill you get it changed. I use them on my bikes all the time dont know if I have a leaking valve but there changed when new tyres are fitted anyway

The pin had come out of my valve, so don't think it was repairable.. it cost me £20 to have the tube replaced, while I waited.. bike was fully loaded with camping gear lol.

The last time I had a puncture a couple of years back I put some tyre-weld in.. it got me home just about, I rode on a flat for the last 1/2 mile or so, again that was another leaking valve.

I've just checked it and it feels like it did when I pumped it up at the garage, very full of air and very hard! I'm going to ride it to a kwikfit to see if it's open and have a look, I wish I knew more about bikes and tyres than I do!                                                                                                                                                                              

If its only flat at the bottom you still need it fixed                                                                                                                                                                              

narr put flat bit to top its ok now ready to go                                                                                                                                                                             

I had exactly the same problem, thought I had a slow puncture and almost paid the garage to change it, then a friend took a look and it turned out to be the valve so he took me to Halfords and I got one from the bicycle department, cost less than a fiver for two, not had a problem since.

Will try that - thanks x