Amazon Prime Video launched its Watch Party feature a few months back in the US and now it has come to the UK, too. At present, it only works via the desktop site but it is available at no extra cost for Prime members.
The service - which is in beta - is like Netflix Party - Teleparty - and includes synchronised playback which the host controls. Naturally, there's a chat feature that you can talk to your friends over, too. Up to 100 people can participate though naturally each will need to have their own Prime
You can go to a specific page on Amazon's UK site to get things started. Find a movie or TV show - that presumably you have already discussed - then click the Watch Party button. Enter your name then click Create Watch Party. You can then share the link via the browser window or click to copy the link so you can paste it into WhatsApp or send via other means.
You can see how many people have joined and then start when people have turned up.
The Watch Party site works on both Mac and PC, but not on Apple's Safari web browser at present. Amazon also warns that if you are trying to do one across international borders that it won't work at present since Amazon US and Amazon UK Prime accounts require you to sign into Amazon.com or Amazon.co.uk, for example.
Even if you all have Amazon UK Prime accounts, eligible content may not be available if you are travelling, for example.