Unveiling a portrait of Dr Chad Varah, the charity's founder, the Prince of Wales said: "I am deeply appreciative and full of admiration of everything these remarkable volunteers do; that you give up so much of your time and provide your love and compassion in this way."
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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.