@Amity Island - Dunno if you have ever tried to collect data in quantity to try and analyse anything but I can assure you that it is not straightforward. Compromises always have to be made and I personally am content that the Met Office are probably in the best position to make them with regard to collecting weather data.
The e-mail you refer to is quite interesting in that it goes to great length to question a small part of the data implying that is enough to invalidate the data set as a whole. Steers very clear of any numerical assessment. Food for the gullible is my assessment.
Global temperatures are rising, a few patched holes in the Met Office data set will not alter that assessment. The logic that this is coincident with increasing industrialisation and burning of fossil fuels is compelling.