Consenting to a sexual act or activity involves agreeing by choice and having the freedom and capacity to make that choice.
A person is free to make a choice if nothing bad would happen to them if they said no. Saying ’yes' to something because you were scared for your life or your safety or for the life or safety of someone you care about is not consent.
Capacity is about whether someone is physically and/or mentally able to make a choice and to understand the consequences of that choice. If you are asleep or unconscious or incapacitated through alcohol or drugs you cannot consent.
If you didn't say the word 'no' or weren't able to speak at all through shock, if you didn't shout or fight or struggle, it doesn't mean you gave your consent.
For more information about consent
Brook: Sexual health and wellbeing for the under 25s