We have lived in three countryside houses in three different counties and found the connections to be rubbish in two of them. Unlike in a town, open reach don’t ‘jump’ when a village is down. I had 45 days down over 2 years in my last house. That includes a tractor taking out a phone pole which pulled out the cable under the field - a specialist wire and team had to be ordered. The previous one, 84 outages in 9 months because someone decided not to bother maintaining any of the sizeable forest around us they owned so the trees rub up against the phone lines (brief outages).
Our saving grace in the last house was being 500 metres from a phone mast. We spent a couple of hundred quid on a modem just for 4G broadband and dumped BT and open reach completely. Ordered a Lebara sim, spent about £25 a month.
The connection is okay where we are but we have had six power cuts in four months instead!!
If you are going proper, property countryside, plan for the worst.
I would have gone starlink if it weren’t for the regular barnies with the other half about giving Elon Musk money.
For 4G internet:
My advice before you take any sort of plunge is to check ofgem’s indoor and outdoor coverage across all networks before even booking a viewing, and when you turn up for the viewing, have a sim from that provider with you, in your phone, and check the signal in the rooms you would want the modem. We did this last time and found 2/3 times that the signal was so weak we couldn’t possibly use it for internet.
(I would probably still just pay Elon Musk but obviously that has moral radar connotations too!)