I've not yet seen any extra police / army presence in the city since the bombings in Manchester but we're now getting asked for bag inspections when entering the Lloyd's building. A few of the newer /bigger office buildings in the city already do this and go further with airport style x-ray machines.
These are interesting times. The city is probably one of the main targets for similar attacks. The last being in 2005 which also included some failed attempts later that month.
I was on the last Euro Star train out of London that day as we were on a works away day(s) to Bruges so missed much of what happened on 7/7. We were also coming back from a team lunch after the failed bombings so had to stay away from the offices for a limited time before getting back to work.
Sadly London will get hit again but more importantly I certainly don't worry about it. There's no point. London is a big place and the chances of something happening to you or someone you might know are tiny. Get on with your life, these extremists will get found and things will get back to normal shortly.