Best to put it into a compost bin and mix. As I do not have a compost bin I always just add it to the borders. As I feed the flowers and plants in the border and mix the soil often-ish I have no problems.

I'd certainly put straight on the garden, it is what we do and we do have compost bins.

I always spread it over the borders in the garden, no sense wasting it, and spreading it out gives you a chance to detect any possible vine weevil grubs present within it - I've never yet found any in mine in 20 years.

you can use it in your tubs for next year if you like.
I "rejuvenate" as much compost from containers as possible, saves a lot of money, and you know what you are getting.

I usually put mine on parts of the garden that need improving. As I often find larvae like cream caterpillars in it, that eat the roots as badly as vine weevils, I tip it out and make sure there aren't any if I want to use it again.

Not recommended practice,Scrumpy... because it may well contain beasties and pathogens which will affect your new plants in containers. I've done it before as well, but its always a risk.

So i take it you replace all your garden soil every year for the same reasons?
I've never had problems with re using compost. Certainly had lots of problems with soil borne fungi in the open ground, and all the other nasties you can think of.
As a matter of interest, a well respected member of the NVS, who writes articles for them on soil and composts and fertilsers, makes his compost for growing prize winning carrots out of compost previously used for growing bedding plants.

I used to reuse it the way you do, but found problems with pansy blight in particular, and something else which affected my surfinia petunias which doesn't happen if I use new compost, no idea what it was. So I no longer reuse it in this way.

The idea of reusing compost is no different to crop rotation in the garden. Obviously, if flowering plants have picked up major bugs whilst growing in the tubs, one would be wary of using that for flowers again.
It would be unlikely that the same bug would affect vegetables, so use it for that. And vice versa.
In the good old days when peat was in abundance and solely used in composts, re-cycling wasn't as critical as now, especially as the modern stuff you buy you haven't a clue what is in it. I don't buy any compost from garden centres now. Either mail order from suppliers who still only do proper stuff, or peat, sand, and sterilised loam and make it up fresh as i go along, and of course re used. Out of about 2000 litres of compost i use each year, i'd say 500 litres is recycled.
The original question was what to do with it.
As a matter of interest, if your container compost had some nasties in it, what would you do with it, as i assume you wouldn't use it on your garden or compost heap because of the bugs you'd introduce.

Yep, I'd still put it on the garden, picking out any vine weevil or chafer grubs. Being in open ground, less likely to cause problems than contained in a pot.

Bamboo, are my cream caterpillars with brown heads chafer grubs then?

Very likely do a quick Google search and you'll see lots of images.

Only if they've got 3 pairs of legs at the front end, Steragram.

Hum - I've had a look and I'm not convinced - these are a good inch long and not curved - they really do look just like caterpillars. Happily I haven't seen any mature ones this year as I caught them when they were just hatched. But we do have the occasional chafer bombing about in the evenings.

Not vine weevil then? They don't have legs, but they are rather shorter and fat. Otherwise, swift moth larvae - they're more white than cream with brown heads and no legs, but more caterpillar like than chafer.

I looked up swift moth larva - yes those are the ones! Mystery solved, thank you. Now I need to know how to prevent the eggs being laid in the pots - some hope - my insect book says the eggs are scattered in flight. What an effortless way of giving birth.

Not necessarily, Steragram, bet it still hurts, lol!