Thames Valley police would not comment on whether any of the suspects reside at the caravan site but said: "This police presence forms part of the investigation following the death of PC Andrew Harper".
Labour leader Jeremy Corbyn also sent his sympathies to PC Harper's family and reflected on the "horror" of the roads officer being killed in the line of duty.
Ten people - including a 13-year-old boy - have been arrested on suspicion of murder after a police officer was killed in Berkshire.
The A4, Bath Road has since re-opened.
Philip Harper also told Sky News "we're in a bad place", after the 28-year-old died following a serious incident on Thursday night near the village of Sulhamstead in Berkshire.
In a video posted on the Thames Valley Police Twitter account on Friday night, Mr Campbell said: "Everybody I've spoken to about Andrew talked about the incredible personality he was, what a fantastic police officer, and what a great friend and man he was, and he'll be sorely missed by everybody".
Prime Minister Boris Johnson has also paid tribute to PC Harper, saying: "I am deeply shocked and appalled by the death of a fearless officer on duty in Thames Valley last night".
Officers remained at the scene of the incident as forensic investigators took photographs of items on the road.
Deputy Chief Constable Jason Hogg said: "As a force we are devastated at the loss of our colleague and will all be supporting each other at this hard time".
"They have my absolute support".
Officers from the West Yorkshire team of the British Transport Police also shared their condolences.
Deputy Police and Crime Commissioner for the Thames Valley, Matthew Barber, said the incident raises the issue of whether officers should be routinely armed.
A total of 10 arrests have been made, and all those who have been arrested are still detained.
Prime Minister Boris Johnson says he is "deeply shocked and appalled" by the death of Thames Valley police officer Andrew Harper.
"Those arrested are all male and are aged between 13 and 30 years of age".
'I would appeal to anyone who witnessed this incident to get in touch.
If you have any information which you think could be at all relevant to the investigation, no matter how insignificant it may seem, visit www.thamesvalley.police.uk/tua/tell-us-about/cor/tell-us-about-existing-case-report/ or call 101.