I had this service activated last July. I do not believe that I have ever had the expected speeds. Checking my talktalk service page shows that speeds appear to be capped at around 48/22 for many months.
I have tested using wifi/ethernet connection/direct connection to the openreach modem and the speeds are almost always 48/22Mbps.
Modem SagemCom FAST 5364, tho I do not believe it is a modem issue