Our neighbour has a fire pit in their garden which they

Our neighbour has a fire pit in their garden which they light every evening throughout the summer when it is not raining. Due to the direction of ch prevailing wind, the smoke from this is always blown into our house and garden. This forces us to leave our garden, go into the house and close all windows and doors. We spoke to the neighbours in person last year, getting the reply "Yeah, we'll bear it in mind". The smoke nuisance continued throughout last summer and we were unable to use our garden in the evenings. Environmental Health came out but said that as the fire pit meet regulations it was fine, completely misunderstanding the complaint we made which was about smoke nuisance and the impact it has on our lives.
The problem has started again and I have emailed the neighbours, reminding them that the prevailing wind blows the smoke over to us and it causes us to change how we live our lives. I asked them to stop using the fire pit and requested that they did not use it this weekend when we will be camping in the garden with our two young children. (having been sworn at, verbally abused and threatened with physical violence when I tried to speak to them in person) . Their reply has come back saying "We are not receptive to threats and ultimatums. We are willing to speak in-person if it is polite and non-threatening, if you wish." The irony is not lost on me! I have said That given the threats made to my self (which led to police involvement last year) I am not willing to speak in person but only communicate by email.
Having read up on the subject it is my understanding that if smoke from a neighbours fire pit, wood burner etc. . prevents you from using your garden and forces you to close windows and doors and generally infringes the right to peaceful enjoyment of your property there is a legal case to answer. Where would we stand on this and how likely would we be to succeed if we took them to court?