Frances Madigan is described as a white Irish woman, 5ft 6ins, who wears glasses and has auburn hair.
When last seen, she was wearing a blue anorak, black trousers, black leather boots and was carrying a black shoulder bag.
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Stamp duty is to be abolished for first-time buyers on properties up to £300,000, Chancellor Philip Hammond has announced in his Budget.
The money will help pay for mental health and counselling services, regeneration in the west London neighbourhood and a new community space.
The small device was hidden in a grate in the ceiling in the only customer toilet at a Starbucks coffee shop.