There were armed officers at Brighton station during rush hour this morning, after Prime Minister Theresa May increased the terror threat to Britain from 'severe' to 'critical' last night.
This follows the attack at Manchester Arena on Monday night which killed 22 people and injured dozens more.
The Prime Minister said around 5,000 troops would be deployed at key sites around the country, to support police.
A Sussex Police spokesman said: "Sussex Police continues to keep all policing under review and in light of the increased threat level we have increased our armed policing (ARV) capability by increasing our current armed officers' shifts to 12 hours. We have also enhanced high visibility policing."