Temperature anomalies over Europe (from GFS) are very interesting. Here is forecast for next 8 days (GFS init today, 06UTC)
(1981-2010 base period, from CFSR reanalysis)
Indeed there is cooler conditions expected in northern parts of UK, but there is huge positive anomaly over Europe with temperatures 6 deg C above normals in some parts. In fact average temperature for this period is higher in eastern Belarus than in northern UK