Thanks for your response. I meant in terms of furthering my career as a teacher of english. Should I get an MA under my belt before doing the DELTA, or do it the other way round? Or does it not really matter all that much?
It would depend on the job you wanted. Also, I can't answer for your local conditions.
If you're teaching English to immigrants to UK, probably the DELTA would be better.
If you're teaching English-speaking undergraduates or High School English, then an MA would be better.
All other things being equal, I'd finish the MA first then do the DELTA - but that's me. The MA is probably more difficult, and I'd want to get it out of the way while I was still motivated to study.
But what I'd really do is contact potential employers and find out how the pay and condition rates differ between what you have and what you are planning to do.
Perhaps another UK person could be more specific.