This is reported by Guardian and Associated Press.
According to media sources, the two countries are set to sign an agreement for a "100-year partnership," covering areas such as defense, science, energy, and trade.
The document aims to deepen defense relations, proposing further military assistance to Kyiv amid concerns that the arrival of Donald Trump in the White House could lead to a reduction in U.S. support.
Starmer is expected to discuss what security guarantees the UK can offer Kyiv, including the potential integration of British troops into post-war peacekeeping forces.
"Putin's ambitions to sever Ukraine from its closest partners have been a monumental strategic failure. At the same time, we are closer than ever, and this partnership will elevate this friendship to a new level," Starmer stated prior to his visit.
Additionally, the new agreement aims to strengthen the economic ties between Ukraine and the UK in non-military sectors. Specifically, Starmer will announce a commitment of £40 million (approximately $48 million) for post-war economic recovery.
The unannounced visit of the British Prime Minister marks his first trip to Ukraine since taking office in July 2024. However, during this time, he has already held talks with Zelensky twice.
Previously, Starmer visited Ukraine in 2023 when he was the opposition leader.