Investment firm Kelso has announced a “new declarable holding” in County Durham-based Filtronic plc, a manufacturer of products for the aerospace, defence, telecoms infrastructure, space and critical communications markets.
Shares of Filtronic have soared more than 200% in the past year to give the firm a stock market value of roughly £650 million.
“Kelso acquired 500,000 ordinary shares in Filtronic at an average price of 185 pence per share between December 2025 and February 2026,” said Kelso.
“Following significant share price appreciation, with Filtronic closing at 296 pence on 24th April, the holding has increased in value and now represents approximately 10 per cent of Kelso’s gross investments, the threshold at which Kelso announces its holdings.
“This has generated an unrealised gain of approximately 60 per cent.”
On the rationale for the investment in Filtronic, Kelso said: “Filtronic’s technological advantage is built on decades of RF (radio-frequency) engineering know-how, a notoriously complex and demanding field of research, a unique technology offering, with in-house chip and module integration, that operates at the limits of power, bandwidth and frequency that can be manufactured at scale.
“Since 2024, Filtronic has announced a strategic partnership and larger follow-on orders with SpaceX, awards from Airbus for satellites on the Eutelsat OneWeb programme, further defence work with Leonardo, additional business linked to the European Space Agency, an RF subsystem contract with QinetiQ and a recent $8.0m contract with another customer for system-level amplifier products.
“This wide range of contracts is testament to the strength of the product suite and demonstrates the broad range of applications.
“The resulting improvement in trading has been significant. Revenue has more than tripled in the past three years and the new manufacturing facility in County Durham provides the capacity to triple revenue again from here.
“As at 30 November 2025, the balance sheet held significant net cash and Filtronic entered the second half of FY2026 with a record order book and approximately 90% of FY26 revenues covered by contracted orders.
“Filtronic combines specialist technology, a stronger balance sheet, clear commercial momentum and exposure to high-growth markets where barriers to entry are high.
“On that basis, Kelso believes Filtronic represents an attractive investment opportunity and will increasingly attract global investors as it continues to develop. Kelso will continue to monitor its investment in Filtronic and engage constructively with the company where appropriate, in line with its investment strategy of actively supporting value creation in its investee companies.”
Kelso chair Nigel Knowles said: “Kelso is pleased to be a shareholder in Filtronic which we believe is one of the most exciting technology companies in the UK. We have great admiration for what the management team has achieved in recent years.
“Filtronic’s success has been hard-earned and is a testament to British engineering excellence. We are excited about the company’s prospects as the space sector continues to develop and as global demand for high-performance radio frequency solutions grows.”
Kelso’s declarable investments are NCC Plc (18%), Saga (16%), CVS (15%), The Works Plc (13%), Selkirk Plc (10%), Filtronic (10%), THG plc (10%) Angling Direct plc (7%). The average market cap of Kelso’s investments is £400 million.