2 metres of cable sounds fine. 5 should be no problem either. The amp shouldn't be right next to the aerial 'cos this can cause interference.
Looking at the picture again, it seems that the whole weight of the aerial is supported by two tywraps round the ends of two elements of the reflector. That seems pathetic. I suppose the tight run of the cable is to stop the aerial sagging too much! And I wonder if the transmitter is *exactly* at 90 degrees to your roof.
Here's some info from the Beeb. They seem a little more forgiving of indoor aerials - if you have a strong signal.
http://www.bbc.co.uk/reception/info/..._tvaerials.pdf
http://www.bbc.co.uk/reception/info/..._digitaltv.pdf
Do you know which is your transmitter:
http://www.dtg.org.uk/retailer/transmitters.html