OMG! Your poor Dad! And You! So very glad Poppy is okay after this incident... I know exactly how it feels... my Biewer slipped out of her harness about our 5th walk, like a professional!
Makes you lose your mind! We had just crossed the busiest street in my neighborhood and we were in the road.
Since that happened, I bought Buddy Belts for all mine, and have not had a reoccurence of slipping out yet... not even close!
I did however find a knock-off company, as two of mine are larger doggies, it was more affordable. The company has a branch in the UK, here's a link... you may want to call them to find a distributor...
Back Bone
Here's a US link for comparison:
Buddy Belts Regular Edition Leather Dog Harnesses
I know with taxes and such it may be best to buy one in the UK...