Why is there this Intrusive /h/ in English accent?

Good question. The phenomenon you're referring to is called aspiration. As you can read in that Wikipedia article, this is when a consonant is followed by a burst of outward breath. (Despite the name, this is not connected to the French « h aspiré ».)

In some languages, aspiration distinguishes two consonants. For example, when we write Sanskrit dharma, it's distinguished from darma, which would be a different word.

However, as with any sound, some languages use aspiration for allophones instead of phonemes. That means it's done automatically in certain contexts, without the speaker even being aware. That's the case in English. Three consonants are aspirated: /p t k/. They are aspirated when they come at the start of a syllable, and the effect is stronger when they're not in a cluster.

English speakers are not aware that they do this. You can sometimes convince them if you have them put their hand at the right distance from their mouth, and then have them say po, to, ko compared with lo, no, ro. They will feel a puff of air on their hand for the first three and not for the last three. This is the beginning of training an English speaker not to aspirate the same consonants when speaking French. I speak from experience...

Meanwhile, to Francophones, the aspiration remains very noticeable since it's not allophonic in French. Your ear is good: it sounds as though there's a burst of air, much like /h/, and it sounds like the rest of the word is delayed by a few milliseconds. Now you know why, but you'll have to live with it as long as you listen to Anglophones. :)