There will be no problem in training with a Class 1 OML and there "should" be no problem in being employed with a Class 1 OML unless you are looking to be employed in the very few situations which are single pilot. A Class 1 OML is after all only the medical equivalent of the MPL which is the aspiration of many new trainees.
The CAA Medical Division will try very hard to help you obtain an unrestricted Class 1 and if you have an opinion from an esteemed cardiologist which will provide additional confidence then tell them so.
I agree,
in theory there should be no issue, but would an employee looking at two equal potential pilots take the one who, according to "the book" could drop dead (now proven otherwise), or the fit and healthy one? The airlines who I've enquired to, usually via a 3rd party such a friend who is a pilot, seem uneasy at giving a firm answer to me.
I am not willing to invest £100k in training with such risks involved with job opportunities, its simply too much. With a firm yes on the medical I'll start my training right away, but until then, its unrealistic for me.