
It does however also explain why your connection is so poor on Three, which is likely to have the least capacity on 4G. And probably where you are also on 3G. Many others in your area will be hitting it hard too. Particularly during what I read is now the peak time, 6-8 pm. I thought it would be longer than that and for you it almost certainly is.
EE is generally the best, with Vodafone also getting some good reports here in contrast to their fixed line service. O2 seems to me to be highly variable for available speeds depending on location.
You could do similar to what I did before ditching my perfectly satisfactory FTTC on cost grounds and went for the 2018 Three Black Friday Unlimited everything deal. I was on a 4G EE low allowance deal for it previously as I didn't really need mobile broadband in those days and had ditched O2 because of its uselessness even for voice and texts in various places I visited. Particularly but not just wide areas of Cornwall.
I bought a £1 Three PAYG SIM from the papershop and stuck a fiver on it for a few days, then took the plunge for my mobile and dropped my FTTC. At the beginning of Jan 2019, having survived the Christmas heavy period, I gave notice on the landline itself. Total saving compared to landline + FTTC + EE contract £49pm.
Since then I bought internet connected security cams so bought the Three HomeFi, as tethering those obviously wouldn't work when I was out of the house! I'm still quids in

My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - Three 4G, tbb tests normally 35-45Mpbs down, 65Mbps off-peak, 9-24 up.
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"Democracy means simply the bludgeoning of the people by the people for the people." Oscar Wilde
Connection - Three 4G, tbb tests normally 35-45Mpbs down, 65Mbps off-peak, 9-24 up.
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"Democracy means simply the bludgeoning of the people by the people for the people." Oscar Wilde