In reply to Oujmik:
Depends how much you value the speed vs. cost and your total monthly usage.
Andrews & Arnold are a very good broadband supplier that aggressively investigate openreach performance on your behalf. If there is more 'speed' to be had out of your line, they will find it. They may also reduce your speed in favour of other improvements (errors or latency) that will make your effective performance better.
Downside is they are quite expensive and most packages have data quotas for daytime use, more generous in the evening and effectively unlimited in the early hours. Maybe 40-60quid a month for fttc fibre package.
They will however sell you a bare copper line with no phone service for 10 a month so you can dump the expensive BT line if you don't actually use the phone. Generally, they request a new length of cable for this, which solves problems too.
They do have a guarantee to take on a existing broadband fault and fix it in 30days or give you your money back. They have never had to.
I have no connection with them other than as a customer. Very impressed. When you call them a network engineer answers the phone after a couple of rings and can actually fix things.
Steve