Nice work Karl. I agree with the chaps. Ordinary masking tape is fine for some tasks, but it is too 'course', which allows the bleed on fine-line work. The Tamiya tape is low tack, smooth, and sharp edged, which helps eliminate the problem. OK, it's about £4, but well worth it, and sometimes you can use the same strips again for less important jobs.
If in doubt about getting bleed-through, once the tape is in place, put a thin coat of the base colour over the edges of the tape; this seals it, and prevents the second colour bleeding and causing the spikey look.