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Once you've come to a stop, you need to assess if it's actually safe enough for you to change your tyre. The Highway Code urges drivers only to “change the tyre if you can do so without putting yourself or others at risk—otherwise call a breakdown service.”
Indeed, you should avoid changing your tyre on the hard shoulder of a motorway or at the side of the road, as you might get in the way of oncoming traffic—leading to catastrophic results. Additionally, if you're driving at night, don't risk changing a tyre in the dark. Even with a reflective vest, oncoming traffic might find you hard to spot. So, if you're not entirely sure it's safe enough for you to change your tyre, call a breakdown service, such as the RAC or the AA. It's always better to be safe than sorry!
If, on the other hand, you've got adequate space and you're sure you're not getting in anyone's way, you're almost at the stage in which you can change your tyre!
What To Do If You Get A Flat Tyre | Resources | PassMeFast
In the UK, you can legally change your tyre on any public land where it is safe to do so. You must ensure that you are not causing any obstruction or endangering the lives of other road users. It is important to be aware of any local bylaws where possible. And pay attention as parking restrictions may apply.
Where can I legally change my tyre in the UK? | Blackcircles.com
