'it drops' as in the connection drops and reconnects and you get these slow speeds - in which case something electrical is being turned on and creating lots of interference (e.g. fluorescent lights, charger for mobile, plasma TV etc etc)
'it drops' as in once school children get home, may mean either
1. Someone is using connection a lot and you are not aware of it (the Asus with its traffic monitor option will show if that's the case)
2. There is congestion at the local exchange, and this is a real possibility
The BT Wholesale speed test with its further diagnostics is useful, as the IP profile will show if its a slow sync speed issue or a throughput issue. If throughput then switching provider might be an answer.