At Tenerife, after dropping off the rescued fishermen, the bow dome began to leak; this continued during her resumed voyage to the Falkland Islands.

Northumberland took up station at South Georgia undertaking fishery protection duties; when this was complete a dry dock was found in Rio de Janeiro that was suitable to carry out a bow dome change.

Deploying to the Caribbean in 1999 for counter narcotics and disaster relief duties, Northumberland seized over two tonnes of cocaine (with a street-value of £135 million), in cooperation with a United States Coast Guard law enforcement detachment.

This refit saw her equipped with an updated suite of weapons and sensors (including a modified 4.5" Gun and the latest Low Frequency Active Sonar) and of propulsion and mechanical systems.

The combination of 2087 LFAS and Merlin ASW helicopter has subsequently proved highly effective and the class is widely regarded as the most capable anti-submarine frigate afloat.

[7] For a time during 2006 Northumberland accompanied the submarine HMS Torbay on her deployment to the US AUTEC (Acoustic Undersea Testing and Evaluation Centre) which is based on Andros Island in the Bahamas.

In 2008, Northumberland deployed to the Indian Ocean as the first RN warship to participate in the EU's counter piracy Operation Atalanta, conducting numerous counter-piracy patrols in the Gulf of Aden and escorting World Food Programme humanitarian shipping between Mombasa and Mogadishu; this was partially documented in the Sky TV programme Ross Kemp in Search of Pirates.

[11] Northumberland eventually returned to Devonport on 5 December 2014 after a deployment which included visits to Gibraltar, Souda Bay in Crete, Bahrain, Dubai and Fujairah in the United Arab Emirates, Mumbai in India, Muscat in Oman, Malta and Lisbon.

[13] A month later, Northumberland moored off Cowes in company with HM Ships Ranger and Smiter to mark the 200th anniversary of the Royal Yacht Squadron.

[16] As part of her re-fit, she was upgraded with Sea Ceptor surface-to-air missiles and returned to sea in 2018[17] In late 2020, with a television crew filming on board,[18] a Russian submarine being tracked in the North Atlantic hit Northumberland's towed sonar, requiring the frigate to abort the 48-hour mission to find the submarine[19] and return to port to replace the sonar.

The ship was previously tasked with patrolling UK waters over the festive period but returned to Devonport so that the crew could isolate, in accordance with health guidelines.

[25] On the 20th November 2024, Defence Secretary John Healey, announced that due to structural damage discovered during her refit Northumberland was uneconomical to repair and would be retired from the fleet by March 2025.