There were 184 rape allegations in 2014, up from 33 in 2009, the National Crime Agency (NCA) said.
It said 85 percent of the rape victims were women and of these, 42 percent were aged between 20 to 29, and 24 percent were between 40 and 49, BBC reported.
Sean Sutton of the NCA's Serious Crime Analysis Section said further work was needed to understand the increase of the situation.
"This initial work clearly raises a lot of questions and we will be working with academia to build a more complete picture," Sutton said.
"Sexual assault is a crime, full stop, and we want victims to feel confident reporting it to the police."
Earlier this month, security firm Symantec warned that almost half of people using dating sites or apps had been scammed or spammed.
It said daters fell victim to blackmail, were subjected to revenge porn and were tricked by people who assumed fake identities to steal cash.