They mean 'total electrical system collapse'. Incredibly irresponsible reporting from the BBC, as sadly we've come to expect.
If somebody reads the first sentence of the article they would know it is electrical though...
plus its prefaced by blackout, so the context is clearly (electrical) system.
Finally it's a headline. You're supposed to read the article before judging whether it's 'irresponsible reporting'
National news outlets should hold themselves to high standards and not be reduced to scummy clickbaiting tactics. And yes, including in headlines; probably, especially headlines. It's disrespectful to the UK public who pay their wages, and irresponsible.
The BBC are absolutely coasting on past reputation.