Visa advice for minor person wishing to enter the UK unaccompanied [duplicate]

I'm assuming that this is a Standard Visitor Visa.

No, you cannot make the trip alone with your current visa.

A letter from your mother doesn't help, because your visa conditions are set by the authority that issues the visa (in this case, that's the UK). Nobody else can remove those conditions.

UK visitor visas for people aged below 18 can be issued for travelling alone or for travelling with an adult. The application requirements are different and you can't convert the latter into the former.

The guidance on the linked page states that if you have a visa for travelling with an adult

you’ll be refused entry to the UK if you arrive in the UK without them.

A consent letter is not a solution, so you need to look for other ideas:

• Persuade your mother to accompany you, and spend the same amount of time in the UK. You do have to be together to travel to and from the UK, but, with her permission, you can do different things while you are there.
• Apply for an unaccompanied minor visa. It is probably too late to get the paperwork together and apply in time for a May trip, so it may need some delay. You would need someone in the UK who can house you and will be responsible for you during your trip. This would be appropriate if, for example, you are visiting a relative who lives in London.
• Delay your trip until you are eighteen, and apply for a simple standard visitor visa. The problem with this is that minors are presumed to be likely to return to where their parents or guardians live. As an adult, you have to independently convince the immigration authorities that you will leave the UK at the end of your trip. That can be very difficult for a young person who is not yet fully integrated into their home country economy and society.