I'm another one who had the dreaded 'twang' when I set off for the drive to Tesco last week. Then I had loud sounds beneath the car whenever I braked or turned sharp right or left, but only at very low speed. I feared the worst. If it was the top mount bearing, I'd probably go for the full suspension rebuild, a broken spring would be more manageable.
Took the car in to my garage this morning. Fixed in five minutes! The plastic undertray had come adrift, and they'd refastened it, no charge. Definite result, and big thanks to Yelverton Garage for sorting me out.