Definitely British Army, circa the First World War. You should try searching for him in "British Army WWI Medal Rolls Index Cards, 1914-1920". If he served in France, Belgium, etc. during World War I, he would have been entitled to the British War Medal and Victory Medal. If he was deployed between 1914 and 1915, he'd also be entitled to either the 1914 Star or the 1914-15 Star. You may also want to try to find his service or pension record here. Although, most were destroyed in the Blitz, so his record may not still be in existence. Good luck!