It is possible to create passport photos and get them printed and delivered for free. It is relatively straightforward - follow the instructions below:
1- Take a picture with a digital camera / phone at high resolution against a suitable background (e.g. smooth bright wall). Guidance for UK passport photos available at https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/303780/Photoguidance_v7.pdf
2- Go to http://www.epassportphoto.com
(other similar website are also available) and follow instructions to upload picture and generate/download passport photos on 6"x4" format (you need to wait 60 seconds before you can download the photo for free)
3- Save passport photos on your phone or tablet
4- Download/install on your mobile/tablet the freeprints app (website http://www.freeprints.co.uk/)
which gives you 45 free 6x4 prints per month (but delivery charges apply)
5- Crucially, when you first sign up with the app, your first order of up to ten 6x4 prints will receive free delivery (£1.49 discount which wipes the delivery cost). You can use this to get your passport photos (and/or other photos) printed and delivered for free!
It is also useful that you can select premium matte paper for your photos rather than glossy. Low gloss or matte paper is recommended for passport photos.
Photos are sent by second class, but you can upgrade to first class for £1. I have uploaded my photos on a Sunday, received dispatch email on Tuesday and photos were delivered on Wednesday (using the free second class option), so in my case the free option was very quick.
The print quality seems fine, if anything photos are slightly darker than I could see on screen.
I hope this is helpful. If you try it, let us know how it goes!