Worth a read..
""When you buy a broadband service from an ISP (Internet Service Provider), they are only responsible for the service delivered to your premises or, at best, to the router.
Also, if you buy a service that offers “up to” a certain speed, that’s basically the best case. It only guarantees that, in the UK, at least 10% of the users of that service get that speed. Most people will get less.
Broadband speeds are reduced by all sorts of factors. These include the distance from the exchange, the quality of the wiring, the number of joints in the wiring, the faceplate, the quality of the router, and the time of day. (You should get faster speeds at midnight than at midday because fewer people will be contending for the available bandwidth.)
The speed measured by a broadband test will also be affected by the state of both the router and the PC used to run the benchmark.
Either way, you can only measure your broadband speed by connecting a device directly to the router using a good quality ethernet cable. Any tests you run over wifi will not give the true speed because wifi connections are slower and less reliable than ethernet connections.""