TRY THIS BROADBAND TEST.
1. Go to www.broadbandspeedchecker.co.uk and click on the speed test bar. Preferably try this during the day. Run the test a number of times and make a note of the average download reading.
2. Remove the front part of your master telephone socket (See picture). Be careful not to disturb the wires. Try all the extension sockets in the house to make sure they are now dead.
3. Connect your router into the back part of the master socket (using the filter as usual) Try to avoid using a telephone extension lead. Now run the Broadband speed check again as in instruction 1.
4. Compare the 2 sets of readings.
If the Broadband speed has increased considerably, then the telephone wiring in your house needs repairing or modifying.