This has only just recently happened, my internet has started becoming extremely slow at night. What's weird is I have my home internet and my mobile phone but they have both started becoming slow at night, is it possible something is interfering with them? (It's just odd that two totally separate things could have the same problem at the same time).
It might be traffic/bandwidth/shaping issues with your ISP.
These are actually more common than most people think.
Also, if you're using a data service over a phone line (eg ADSL), it may just be that your telephone pair runs next to some others in the feedercable which are causing distortion on yours, that would usually result in deteriorated SNR values and downsyncing. Your ISP should be able to check that for you if you call them at a time when the problem occurs.
Also, when using ADSL, I've heard of other electrical appliances causing interference on the phone line, from tv's to washing machines and the likes.
So if you have access to sync-values in your modem, check those out (you can post them here if you don't know how to interpret them).
If the sync values are alright, do some speedtests (speedtest.net) during the day when it's fine and during the night when it's slow and send those to your ISP.
Most ISP's need some convincing before they will act, as it involves spending money to create more bandwidth.
If you're using Cable, you're sharing the loop with your street. ADSL connections go straight into the DSLAM. Bandwidth can be guaranteed on ADSL and not on Cable.
If you have an ADSL slowdown, you need to contact your ISP who can then chase the line provider.
If you have a Cable slowdown, you're pretty much stuck.
Kbw, that's not entirely correct.
The bandwidth after the DSLAM, where lots of ADSL ISP's use ATM, can be heavily reduced if the VP you're on is overloaded.
I've actually seen that happen on quite a large scale as a result of bad monitoring.
That's the problem usually with ADSL, the ISP blames the line provider and they in turn blame the ISP for these kinds of issues, which is why I urged him to get some sync details and speedtests done.