I had BT Infinity installed in June, the up to 76mb package. Afterwards, when ever I took a speedtest.net test I would get between 74-75mb download speeds.

However yesterday and today some BT engineers have been opening up the green box on my road and spending all day doing stuff to it. My internet kept cutting out while they were working on it but they've gone now, obviously they've finished what ever they were doing.

However my download speed now is always 30mb when I test it. Does anyone know why they would lower my speed, especially considering I'm paying for the higher speed? Legally can they do that?

It wasn't malicious so yes they can legally make your line disconnect and then operate at a lower speed, as long as it's accidental as they say they don't throttle anymore. This has happened because the constant disconnects during their maintenance or whatever they were doing made the system think your line had a fault, reducing the maximum speed it can operate at. You may find it will go back up in 5 days or so of its own accord. Or you may need to phone BT to reset the DLM on the line so it will train back to the higher speed.

Cheers pal for the helpful and quick answer

turn the modem off and give it 5 minutes

Absolutely do not do this. Keep the modem connected.

DLM has kicked in on your line - the system thinks your line is having trouble connecting and has automatically reduced your speed to increase stability. If you continue to switch the modem on and off, it will think there are still problems and cut the speed even further!

Leave the modem connected, after a week or so your speed will rise.

This may take longer - my Infinity used to cut off when it rained, and I had to have a new phone line from the pole to my house. It took about a month for the speeds to recover to maximum, as it increases incrementally over time.

If a limit has been imposed on your Infinity line then, unlike normal broadband there's no automated process to get it back up to speed, again, happened to me, you may need to log a call with BT when someone will manually take the limit off.

Sorry - but you're wrong about this. In the vast majority of cases, DLM will increase your speed again as soon as the line has been stable for a period of time.

As I said in my post - my speed dropped due to a fault, the line was replaced, and my speed had been cut from 80mbps to 60. It took a full month after my line was reconnected, but my speed recovered via DLM with no action on my part.

A profile reset is very hard for an ISP to do, and is only done in very specific cases. This is very much the exception to the rule.

Check the BTCare forums for more info on this. https://community.bt.com/t5/BT-Infin...d/td-p/1074898

For a one off drop in speed the BT Openreach advice is to power cycle the active NTE5, that's the VDSL modem to me and you.

For the DLM to kick in it takes much more than the odd user initiated reboot.