10p

According to Paterson in 1989, the cost of a phone call was 10p. (TV: Survival)

The bigger 10p pieces stopped being legal tender around a decade before 2004, around the mid-1990s. The Ninth Doctor tried to use these 10p pieces to pay for a cup of tea in a café in Cambridge. (PROSE: Have You Seen This Man?)

The Fifth Corsair's Ouroboros tattoo was the size of a ten pence piece and located on her upper thigh. (PROSE: Eleven Things You Probably Didn't Know About the Corsair)

Information from invalid sources
A takeaway which Ryan Sinclair once visited sold gravy for 10p. (NOTVALID: The Universe is Calling)