As I will be on a pay monthly no contract connection, will be free to change anytime.

As far as the line is concerned, I have had O.R. to attend multiple times.

Pairs have been swapped to no avail.

Similar to many of my neighbours.

I am concerned that they may deem the line as unfit for broadband.

Also 4G can be very poor at times.

Have attempted for a Virgin Cable install, but after nearly 5 yrs, they have stated it will be not economically viable.

I expect you didn't follow jelv's link. You should. It's "interesting", but not in the way you'd think .

Yep, I did look at it, better speeds than my line.

Ouch!