I'm a BT engineer and most of my work is broadband faults and testing, The white/silver Netgear routers are not very reliable, alot of it is down to people leaving them turned on 24-7, they do get quite hot, and people usually sit them were there not seen so they tend to over heat.
Another thing is the amount of extensions and DSL filters that are fitted, the more that are plugged in the slower the ADSL speed.
I did a test on my home line, with 5 extension and DSL filters i was getting 3.2Mb after removing all the extension etc i was getting 5.5Mb.
If you only have 1 socket i'd try a different modem or router.