I have dug out my old 2820n router and flashed the firmware to the most recent version.

According to my old router, a Sky SR102, I was getting on average a 3mbps download speed which was also confirmed by the Speedtest app.

Since changing to my 2820n, the Speedtest app is reporting 1.6mbps.

I have nothing complex setup on the router but was wondering if anyone else had had similar issues with routers.

You may need to change the ADSL modem code.