There's a free app called Librelink which is approved by the libre makers. The phone needs to be Android with NFC so it can read the sensor. I'm pretty sure you can buy just a sensor for £50 and start it with the free Librelink app on phone - see footnote 4 on librelink webpage, sorry not too good with phones so can't link, google it.
To be honest, phone app can be a bit clunky reading the sensor: looks a bit nerdy waving a large phone around at my arm in public with it lit up and buzzing, whereas reader (one off cost of £57) is more discrete, palm sized, no buzzing.
Some hospitals give out a free reader and one sensor for a trial run and you then get to keep the reader and can use it with any new sensors you buy, but it depends on the hospital, not all do this, but no harm in asking. Two people I work with started this way.
You're not tied into any sort of contract so you wouldn't be committed to £100 pm. A lot of people just buy a £50 sensor now and then for a detailed two week peek rather than using it all the time.
Don't expect it to be the same as a blood test. They're measuring two different things, related but still different. They'll generally be in the same ballpark. The reason I love it is that with finger tests, you're getting 5 to 10 'snapshots' a day, whereas the libre shows you the whole movie. It's one thing knowing you're at, say 5 or 6, but it's much more useful to know where it's been and where it's going - libre shows you that. I've had lots of situations where the libre tells me not only that I'm at 5 but also that I'm dropping hard, so I can eat and stop the hypo before it even happens. It's like being able to change the future. Just can't do that with strips.
Abbott are pushing for it to be on NHS. I think it will be eventually. There was probably the same political hassle when we moved from colour changing test strips (still remember being told to cut them in half to save money) to funky digital meters. Politicians are pretending they are not satisfied of the clinical benefits but it's just really the cost.Sorry, rant over...