UPDATE
Visited the hospital yesterday for the appointment and, as expected, I will have to go in for surgery now as it's the only way to effectively get rid of it once and for all.
I don't know of the date yet when I'm going in, but when we was talking about it the specialist revealed that the method that will be used to get rid of the sinus is full-excision which removes the sinus and some of the skin around it and ensure that the chances of re-occurrence are virtually zero. This will take about 2 to 3 months to heal and when I mentioned the flights in May to Spain I have booked he didn't particularly like the sound of, which to me suggested that the flights have to be cancelled (won't get the money back from the airlines so if it comes to that I'm guessing travel insurance will cover this?).
The more I think about it the more I wish I was referred for surgery last November (after I had finished the second round of antibiotics) which I was in favour with all along, and although it would've possibly meant an uncomfortable Christmas had the operation fallen before/during/after the festive period, it certainly wouldn't have put any plans I had in advance at risk.
I will keep you all updated on when this will be, and the events leading up to it and the aftermath.
For those who may want to know more
I've found this site to be a useful source of information.