For non-urgent police enquiries call 101 or in an emergency always call 999
Examples of a concern for welfare would be a neighbour not been seen for a number of days, a vulnerable relative who has been buying expensive presents for an associate, or a child who is left home alone etc.
If you have concerns for someone's welfare and believe they may be in immediate danger, or at risk, contact the police to report this on 999.
If appropriate, you should also try to make contact with any relevant agencies that are involved with the person. e.g. social worker, carer.
If you have concerns for someone who is having suicidal thoughts, help can be obtained from NHS.
You should also contact the NHS if you have concerns for someone in relation to their mental health, and are unable to contact their support worker, by visiting the NHS website or by calling 111.
If your concern is regarding domestic abuse, you are able to report this online to the police, here.