Told you it was cold
The first 16 days of June have not only been on the cold side over the British Isles but also over, large parts of the United States and eastern Canada with anomalies of -4°C below the 1948-2014 LTA over the Great Lakes. Meanwhile over a swathe of central and eastern Europe, stretching from southern Italy in the south to Finland in the north, mean temperatures have been as much as 5°C above average.
There’s no problem finding the cause of the cold start to June if you examine the mean MSLP for the first part of June. As you can see there are large positive anomalies over Greenland (+17 hPa) and eastern Russia (+8 hPa), and negative anomalies over the British Isles (-6 hPa) and east of Hudson Bay (-2 hPa).