Their demands are made amid a new analysis of test providers, which the party says shows "the spiralling prices" facing British travellers this summer.
According to Lib Dem research, of the 400-plus providers that meet government testing standards, 102 firms (24%) charge £200 or more, while only 47 offer tests for (11%) less than £50.
The most expensive test comes is currently priced at £575, offered by a provider in London.
In comparison, Greece and Italy have capped prices at £34 and £52 - while in France, tests are provided for free.
