I would not even say "ancestors" to them and here is why, the horse in Bronze Age Ireland and Britain was very rare and they were even rare on these islands in the Iron Age.
"The ancient horse remains were all grouped in haplogroup A. There was a major clustering when the ancient sequences were compared to the modern sequences; this suggests that the ancient sequences did not reflect the distribution of the modern day horse populations. This can then imply that an ancient haplogroup has been lost during evolution.
By Katelyn Belz"