No, they're extremely effective in the "SLAPP" sense, because you have to be able to prove the truth in court against perjuring witnesses, and you have to be able to pay for it.

To take a justified example where a ""journalist"" really did defame someone: https://www.independent.co.uk/news/uk/home-news/katie-hopkin...

"This includes £24,000 in damages to Monroe and £107,000 to her lawyers to cover court costs." Hopkins is now selling her house to cover costs.

Most people fold immediately when threatened with a convincing libel suit, because apologising (even for the truth) is a lot cheaper than a settlement which is in turn a lot cheaper than losing your house.

Another high profile example of effectively suppressing true facts: Trafigura https://www.theguardian.com/environment/georgemonbiot/2009/s...

Note that a litigant doesn't necessarily have to suppress facts forever, a few years while the case proceeds is often enough to turn the original issue into a historical curiosity.

To give context to all of the surrounding links, which are all about libel in the UK, remember that truth is not an absolute defense to libel in the UK. In addition, the burdens of evidence are different.