It is possible to include an OS map in a popup window, although not recommended. This has been tested with two different popup builders with differing results. The problem with all popup windows is that the map needs to be redrawn when the popup opens, and most of them will consume map tiles even if the popup is not opened.
Popup Maker
Popup Maker is supported in OS Datahub maps. This one works by looking for a CSS selector on elements within the page, so by adding a CSS selector to any button, image, text, etc. you can convert that item into something which will open a popup. The downside of this approach is that every popup definition has to be loaded on every page of your website. If you have one map that may be no hardship, but if you have hundreds then it will add a lot of bloat. It may also add to your tile consumption because even a popup which is not open will consume two or three tiles, and that happens for every single page open regardless of whether a map is displayed.
To ensure that Popup Maker maps are properly redrawn you need to add popup=pum to the OS maps shortcode.
Popup Builder
Popup Builder does not have any specific support in OS Datahub maps, but it appears to work for simple maps specified by a single location. It does not work for auto-fit maps based on GPX files.
It uses the same CSS selector method as Popup Maker, so suffers the same disadvantages.
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