In theory, though that one is missing the common Openreach logo.
If a new property it may have http://www.kitz.co.uk/adsl/images/phone/external_NTE...
on the outside, and all the internal stuff is done by the builder (and of suspect quality sometimes)
adds a few words, in short no easy testing situation in this situation.
For the original poster, it is a case of a methodical approach and deduction, e.g. disconnecting parts to try and figure out what is happening. At the simplest level a photo of the back of one of the silver plates will help, and if it has three wires, one to pin 2, one to pin 3 and one to pin 5, lift out the one on pin 3 at all sockets this may improve speeds.