Europol said it had seen “increased online activity by those seeking child abuse material”.
The UK will cease to belong to Europol, which helps member states combat serious international crime and terrorism, once the transition period for leaving the EU ends.
Christine Jardine, the Lib Dem home affairs spokesperson, who wrote the letter to the home secretary, said: “A terrible and disturbing aspect of this pandemic is that illegal activity online, including child abuse, appears to be escalating.