I myself use a wheelchair. There are several automatic door closers available for wheelchair users, and these days quite a few of them also have Alexa integrations. 
So the devices definitely exist.
The issue is all of the needed safety features to keep from crushing a person or pet. They add significantly to the cost. Expect to spend about £500 for the least expensive for an exterior door. For someone in a wheelchair, very much worth it. Others will have to make their own determinations.
Also, again for safety reasons, these doors both open and close quite slowly, about the same speed as a garage door. So that’s just something to be aware of.
Because of the safety issues, I strongly recommend buying a purpose built device, then integrating it. Any model which allows for a button control is fairly easy to splice a smart relay into. (Although these days an Alexa integration is often simpler.)
Olide is a good brand, widely available in both the US and U.K…
Autoslide, also available in both the US AND UK, is probably best for sliding glass doors.
Dorma is another brand available in the U.K., but they are intended for professional installation and don’t sell all in one DIY packs as Olide does, instead you have to order all the individual parts.
Mantion, Topp, and other EU brands are also intended for professional installation.
(In the US, there are other DIY brands, particularly SkylinkNet’s Ottodoor.)
Anyway, start by looking for wheelchair doors and you should find a few choices.
(BTW, you are responding to a post which is 7 years old, and a great deal has changed in that time. In the future I suggest you look for more current topics, particularly when it comes to device selection. Or start your own topic under projects and you should gets lots of responses.
https://community.smartthings.com/c/projects-stories
Make sure you put U.K. in the thread title as device selection does vary somewhat.)