I have submitted an illustrated article to a national UK paper, and they are going to publish it this week. What is the situation about submitting the same illustrated article to other publications. Is submitting to direct competitors not done? Could I submit article same article to, say, magazines OK?
They should have sent you an agreement. If it's a paid-for article they may hold some copyright, and that detail would be in the agreement. If it's unpaid, strictly speaking you should retain copyright, which means you can do what you want with your writing. However, you should still have some sort of agreement which will specify whether the publishers expect exclusivity, and if so over what period of time.
I'd just be careful about multiple submissions because it would be a shame to upset a possible source of further work if they judge the article a success but were expecting sole use.