Events to mark Armed Forces Day have taken place across the country, including a celebration at Guildford attended by David Cameron.
Speaking at the national event, which included a service at Guildford Cathedral and a parade of more than 900 service personnel, veterans and cadets, the Prime Minister said: "Today, we celebrate our brave servicemen and women who work so hard to keep our country safe."
Police had encouraged the public to attend events as normal after it was reported that a parade had been targeted by Islamic State (IS).
The suicide blast, planned for a parade in south-west London, was intended to strike at soldiers from the unit of murdered Lee Rigby, according to The Sun.
The newspaper said the plot to bomb the parade in Merton was thwarted when it told police and security services about it.
Other guests at the Guildford event included Defence Secretary Michael Fallon and Vice Chief of the Defence Staff Air Chief Marshal Sir Stuart Peach.
The Duke of York took the salute on the parade route on behalf of the Queen and Royal Family, as the Red Arrows staged a fly-past.
More than 150 other celebrations taking place to mark the seventh annual Armed Forces Day ranged from large-scale parades to simple community events.
They took place against a backdrop of heightened security in the aftermath of the Tunisian beach massacre. At least eight Britons are among the 39 holidaymakers killed, the country's ministry of health has confirmed.
A Scotland Yard spokesman said: "The police, together with our security partners, remain alert to terrorist threats that may manifest here or where individuals overseas may seek to direct or inspire others to commit attacks in and against the UK.
"It is always helpful when journalists share with us information, as The Sun did in this case, that could indicate terrorist or criminal activity."
The spokesman continued: "While the UK threat level from international terrorism remains severe, we would like to reassure the public that we constantly review security plans for public events, taking into account specific intelligence and the wider threat.
"Our priority is the safety and security for all those attending or involved, the public are encouraged to continue with their plans to attend or take part in events as normal.
"We would also like to reiterate our long-standing advice to remain vigilant and alert. As ever we would urge the public to get in touch to report anything suspicious by calling the confidential anti-terrorist hotline on 0800 789 321 or in an emergency by calling 999."