The statutory definition of consent in the UK states that to consent a person must agree by choice, and have the freedom and capacity to make that choice. If a person agrees to sexual activity due to fear for their safety or fear of the consequences of saying no, that is not consent. If a person is asleep, unconscious, or incapacitated due to alcohol or drugs, they are not able to give consent. Consent must be voluntary, explicit, and obtained prior to any and all sexual activity – if you consented to sexual activity with an individual in the past, this does not mean you automatically consent to any future sexual activity.
This short video helps explain consent in a way that is easy to understand: