They will be unable independently to trace you, and will have to apply to the HFEA for release of any information.
The Human Fertilisation & Embryology Authority (HFEA) is required by law to keep a register of all donors.
Any child conceived through your donation has the legal right to contact the HFEA for non-identifying information when they reach 16 years of age. When they reach 18, they can request identifying information about you, including your most recent address on the HFEA register.
You will be given written notice that they are requesting this before your details are released.
It is generally considered to be in the best interests of a child that they have the right to know about their identity, and that is what the register is there for.