Apologies Lebara runs on Vodafone network, most of the info is on their website. Check the coverage for your area though.
We get poor signal in our area on most networks, we choose this one as was the best one for us, is also got WiFI Calling (VoLTE) that works very well using your own home wifi.
They are cheap, not had any issues so far but with the short contracts you can at least test and then leave it its no good for you.
https://mobile.lebara.com/gb/en/rates
Service and network coverage can be checked here
https://mobile.lebara.com/gb/en/network-coverage