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A new festival at Kew Gardens is promoting the thousands of edible plants on display.
The IncrEdibles festival opens on Saturday and runs until November.
Far-right organisation English Defence League has called on its supporters to gather in Woolwich to protest in response to today's attack.
Leading members have called for people to "take to the streets" and asked them to join a local division of the organisation.
One message, posted online, asked members to get to London "...now if possible."
London mayor Boris Johnson said it was "overwhelmingly likely" an attack in south London in which a man was hacked to death was an act of terror.
"Obviously it's early to have all the facts ... I am afraid it is overwhelmingly likely now to be a terrorist attack, the kind the city has seen before," he said in televised remarks.
Two men have been arrested after separate attacks on mosques following the terrorist incident in Woolwich.
A 43-year-old man is in custody on suspicion of attempted arson after reportedly walking into a mosque with a knife in Braintree, Essex.
Local MP Brooks Newmark tweeted:
Just met with leaders of local mosque in Braintree which was attacked this evening. Thanked local police for their swift response.From @TweetBrooks on Twitter:
Essex Police confirmed a 43-year-old from Braintree had been arrested on suspicion of possession of an offensive weapon and attempted arson after the incident.
Meanwhile police in Kent were called to reports of criminal damage at a mosque in Canterbury Street, Gillingham.
A spokesman said a man is in custody on suspicion of racially-aggravated criminal damage.
Two people have been arrested in connection with a murder in Woolwich today.
Metropolitan Police commissioner Sir Bernard Hogan-Howe said:
It is hard to comprehend the shocking and horrific scenes we have seen this afternoon on a busy street as Londoners went about their day as normal.
We have launched a murder investigation, being led by the Counter Terrorism Command. Two men have been arrested in connection with that murder.
We understand concern about the motivation and we will work tirelessly to uncover why this occurred and who was responsible. I understand people want answers, but I must stress we are in the early stages of investigations.
– Bernard Hogan-Howe
I would urge everyone to remain calm and have a measured response to today's tragic events.
In Greenwich we have met with community representatives, and extra officers remain on duty there tonight.
Across London our officers are in contact with their communities too. The shock that we all feel at what has happened must bind us together.
Around 40 members of the far-right organisation the English Defence League have run towards police in Woolwich following today's attack in the area.
Officers are now flooding the streets after the organisation called on its members to meet in the area to stage a protest.
Met Police Commissioner Bernard Hogan-Howe said two men have been arrested in connection with a murder in Woolwich today.
London's children are still increasingly at risk as a new report finds close to half of them cannot swim.
The Amateur Swimming Association also found that only 2% of schools deliver the Governments recommended delivery time for school swimming, which is 22 hrs.
Labour leader Ed Miliband said the killing of a man in Woolwich is a "truly appalling murder".
Mr Miliband, cutting short a Germany visit to return to the UK, said his party offered the Government " complete support".
He said: "This is a truly appalling murder which will shock the entire country.
“All of my thoughts are with the family and friends of the victim.
“The British people will be horrified by what has happened in Woolwich. Theywill be united in believing that this terror on our streets cannot be allowedto stand.
“The Labour Party will offer the Government our complete support in establishing the facts of what happened and ensuring that those responsible face the full force of British justice."