.. I've accidentally pushed the pin right out.....

And I cannot get the blummin' thing back in, it's just too fiddly....

Any tips ?

Time for a quick link. Most newer 8 speed and above chains should not reuse the pin anyway

How many speeds is your chain? And do you happen to know the brand on the chain?

Don't push the pin back in, btw. Most chains aren't made to be opened and closed that way anymore. I would buy a connecting link of the correct width. KMC makes them for 6-speed on up.

If the chain is long enough you could remove the link with the missing pin, push out the next pin on the next link and use that.

Only if the chain is 6-speed or less. 7-speed and above should not reuse a standard pin.

Chain is a KMC 8 speed. I may try & remove a link.

Cannot easily get a quick link where I live, and I want to be back on the bike.

Not saying you are wrong but i have succesfully done it with Shimano 9 speeds chains a number of times. So i presumed an 8 speed chain and below would also work.

10,11 speed i know would not work.

But yes a new pin or quick link is a safer bet overall.

Yup done that now. I'll see how it goes.

Well, it's certainly not recommended. A light rider in moderate terrain is more likely to get away with reusing a pin on narrow chains than a heavy rider riding big hills. To me it's not worth the risk.

Follow on question - if I decide to buy a new chain, how likely is it that the rear sprockets / front chain rings are worn with the old chain and they will not run smoothly with a replacement chain ...?

(Edit - chain is the original when I bought the bike & that's more than 12 years ago, I currently do between 1000 & 2000 km a year, although a few years ago that figure would have been lower.)

Oh dear... shortened chain means I cannot change to lowest gear without the cage touching the sprocket.

As a temp fix, you can adjust the limit screw to block that gear so that you don't shift into it by accident.

Kept any of your older chains? Until you can get a new one, get a link from it.

Older chains ? This is the only one the bike has had.

So... err....how likely is it that the rear sprockets / front chain rings are worn with the old chain and they will not run smoothly with a replacement chain ...?

Chain is the original when I bought the bike, reckon it has done between 10 and 15,000 km.

That is a hard call. I'd just buy a chain at a local bike shop. If you then see issues that are common to worn cogs, then get the freewheel, cassette or chain wheels as needed. If money is no object, remove the seat and put a new bike under it.