I believe the 6th Battalion Royal Berks was raised in Shorncliffe, Folkestone in Sept 1914 and moved to Colchester in Oct 1914 until May 1915 and then on to Salisbury Plain.
The trees in the background of the photo look like they are bare in winter. This would indicate the location is Colchester. The use of the leather 1903 pattern ammunition bandolier also suggests the photo is in 1914/15 before being equipped with 1908 pattern webbing equipment for use in France where the 6th arrived in July 1915.