Which network? There are 4 physical networks, try all of them. If you are using a virtual provider (Tesco, Virgin Mobile, ID mobile etc) then try the real networks.
At home, I can get 70mbps from EE, and 30mbps from Vodafone, but only 10 or 15 mbps from Three. But moving to the other end of my (long) road, the whole thing changes, and Vodafone can provide over 90mbps, and EE only 40mbps.
If you have an unlocked phone get prepay SIMs from them all:
* EE
* Three
* Vodafone
* O2
Prepay SIMs are often in petrol stations for £1 without any credit, will show if you have a signal. Doing a speed test often requires credit, so cheapest way is to find a friend using the network you are interested in.
plusnet 80/20 (2/jun/14) at 470m - Sync history highest: 64/9 (Sep/17), 54/6 (Jan/19), 51/6 (Mar/19)
20 years of broadband from 1999's ntl:cable modem trial - Live BQM