The open and shut buildings checklist

1 Westminster School, London: 'Strictly private - no entry unless on school business,' says a sign at the entrance to this boys' private school. Security is limited to the bursar and the school porters. I walked past the bursar into classrooms, a kitchen and the music centre. A teacher finally asked if he could help after 10 minutes. Tristram Jones-Parry, the under-master, admitted the measures were 'not foolproof'.

2 Greycoat Hospital, London: Comprehensive school with two security cameras, an entryphone at the back and a caretaker at the front with a TV monitor. The caretaker was away from his post, so I went to the second-floor library. 'I would have expected staff to challenge you,' said Richard Cooper, the deputy head.

3 St Ermin's Hotel, London: Security men on patrol and security cameras in the lobby. The hotel plans to install magnetic cards for bedrooms. I took a lift to the sixth floor, walked the length of the corridor and roamed the Caxton bar, the ballroom, and Clarence and York function rooms. The only response: a member of staff who said hello. Colin Wakefield, the general manager, said that more security cameras were being introduced.

4 St Thomas's Hospital, London: Here, where baby Alexandra Griffiths was snatched in January 1990, security guards stand under a reception banner proclaiming 'We're here to help you.' Banks of TV screens monitor all entrances. I went to the sixth floor of the north wing into wards without being challenged. 'It's a public building. There's only so much we can do, but you should have been challenged,' said a staff member.

5 Credit Agricole building, Fleet Street, London: Tight security, disguised as help, at the 'reception' of this French bank. All doors are locked by an electromagnetic panel which can only opened by a staff pass. Visitors must be vouched for and are escorted everywhere.

6 Goldman Sachs Building, Fleet Street, London: After just a few steps into the foyer of this US investment house building, security pounces.

7 Department of Health building, Quarry House, Leeds: Impossible to get further than the reception of this building, which houses civil servants. After a request for my pass from the military-looking security guard, a mobile-phone conversation led to the appearance of three other guards. The photographer and I were escorted off the premises.

8 St James's Hospital, Leeds: I managed to get into wards leading to the liver transplant unit. Entrance to the pharmacy requires a card pass, but its door is kept open on a suction pad for two minutes, so when someone walked in I followed.

9 Leeds Grammar School: This private boys' school employs uniformed guards carrying two-way radios, but I walked past, wandered down a corridor, past the prefects' office, and into a classroom. The deputy head said they expected all normal people to report to reception.

10 Biochemistry department, University of Leeds: I bypassed reception and went to room 40b B1 filled with test-tubes and computers. A notice said 'Supervised area: no unauthorised entry. Radioactive area open source.' A researcher came in and smiled. But in reporting ourselves, guards swooped, and ordered us out.

11 Princess Grace Hospital, London: Implacable security staff guard this private hospital. Impossible to sneak past reception. Timothy Blow, the hotel services manager, said they took security seriously but 'we have to be careful not to offend our regular visitors by being heavy-handed'.

12 The Bank of England: The only way in is a narrow walkway. A gatekeeper in full regalia asks if he can help two steps in. If you attempt to walk past he will block your way. Two plain-clothes security men are immediately behind him. Another gatekeeper is not far behind, and two more sit on reception. All bags are searched and visitors are escorted everywhere.

13 The Stock Exchange: The lobby is public but beyond that is barred to visitors. Security measures include closed-circuit TV. Visitors are signed in and escorted around revolving doors to stop anyone bursting in.

14 Claridges: Corridors were deserted and several doors open. But later a Claridges spokeswoman said I had been observed on film between 13.09.54secs and 13.32.12secs.

15 Biotechnology department, Imperial College London: Most doors were locked but room 190 - a fermentation laboratory containing poisonous substances - had been left open with no one there. A spokeswoman said: 'The building is an open one and we don't want to make the institution into Fort Knox.'

(Photographs omitted)