Helicopters patrol from the air, armed police on the ground are on high alert and extra security barriers are in place around Buckingham Palace as London .
Following the Brussels attacks which hit the city's international airport and a metro station last month, security measures have been stepped up at all major .
The blasts in Brussels have triggered a wave of security alerts across Europe. Germany, France, the Netherlands and Denmark have stepped up and .
After the Paris attacks, the European Parliament has stepped up its security measures in Brussels and Strasbourg. Security is also tight ahead for Strasbourg's .
