Now in Grub Street Cutting - long story but we are moored within the cutting, after having driven some of it backwards - and the results are interesting, because we are "on the edge" of internet connectivity:
iPhone (Talk.home) within boat..............................no connection
iPhone outside of boat..............................................10Mbps
Mifi router, Giffgaff (vertical aerials).....................10MBps
Mifi router, Lycamobile (horizontal aerials)........no connection
Mifi router, Lycamobile (vertical aerials).............7Mbps
So it goes to show 1) EE isn't always the best signal, sometimes O2 or another is, 2) horizontal aerial position isn't always best, sometimes its vertical, 3) its not possible to rely on tethering to a phone within the boat.