If this page is correct, you are about 2 to 3 weeks away from your first frost, so you should be fine. https://www.plantmaps.com/interactive-united-kingdom-first-frost-date-map.php

My notes on planting and growing garlic: I've always followed the rule of planting a couple of weeks before your first frost and then mulch over it. What happens is those first couple of weeks allows the garlic to establish roots and make a nice home for itself. Then the frost comes and the bulbs will focus on developing roots and not try to grow upwards. Once winter is over, everything underground should be well established and the shoots should start to pop up with the warmer weather. Keep it watered through spring and prune off the scapes (tail like growths from the center of the stalks with a pointy bulb on the end). Stop watering in early to mid summer, a couple of weeks before you plan to harvest. Once about 1/2 to 1/3 of the leaves have turned brown, you're ready to harvest.