https://insidegovuk.blog.gov.uk/2013/07/10/whats-the-max-file-size-for-attachment-uploads/

What's the max file size for attachment uploads?

The information in this blogpost may now be out of date. See the current GOV.UK content and publishing guidance.

We get asked this a lot.

The answer is 500 Mb - which is way more than you should ever need, and obviously you should be trying to keep file sizes well below this.

If you need to upload bigger files than that, or if you find you are having trouble uploading ones that are within this limit, then let us know using the support form.