Wikipedia: Communication is the activity of conveying information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast distances in time and space. Communication requires that the communicating parties share an area of communicative commonality. The communication process is complete once the receiver has understood the sender.
So if you are communicating in the below circumstances (audible warning) it is not illegal:
- and The Highway Code is guidance - not law.
Regulation 99 of the Road Vehicles (Construction and Use) Regulations 1986 provides for the use of audible warning instruments. It states:-
99(1) Subject to the following paragraphs, no person shall sound, or cause or permit to be sounded, any horn, gong, bell or siren fitted to or carried on a vehicle which is
(a) stationary on a road, at any time, other than at times of danger due to another moving vehicle on or near the road; or
(b) in motion on a restricted road, between 23.30 hours and 07.00 hours in the following morning,
unless provided for by the following paragraphs.
NOTES:
(i) A road is a restricted road for the purpose of this paragraph if there is provided on it a system of street lighting furnished by means of lamps placed not more than 200 yards apart.
(ii) Paragraph (1)(a) does not apply in respect of the sounding of a reversing alarm when the vehicle to which it is fitted is about to move backwards and its engine is running or in respect of the sounding of a boarding aid alarm.
99(3) No person shall sound, or cause or permit to be sounded, on a road any reversing alarm or boarding aid alarm fitted to a vehicle-
(a) unless the vehicle is a goods vehicle which has a maximum gross weight not less than 2000 kg, a bus, engineering plant, a refuse vehicle, or a works truck;or
(b) if the sound of the alarm is likely to be confused with a sound emitted in the operation of a pedestrian crossing established, or having effect as if established, under Part III of the Road Traffic Regulation Act 1984.
(4) No person shall sound, or cause or permit to be sounded a gong, bell, siren or two-tone horn, fitted to or otherwise carried on a vehicle (whether it is stationary or not), unless provided for in the following paragraphs.
(5) Nothing in paragraph (1) or (4) shall prevent the sounding of
(a) an instrument or apparatus fitted to, or otherwise carried on, a vehicle at a time when the vehicle is being used for one of the purposes specified in
regulation 37(5) and it is necessary or desirable to do so either to indicate to other road users the urgency of the purposes for which the vehicle is being used, or to warn other road users of the presence of the vehicle on the road; or
(b) a horn (not being a two-tone horn), bell, gong or siren
(i) to raise alarm as to the theft or attempted theft of the vehicle or its contents; or
(ii) in the case of a bus, to summon help for the driver, the conductor or an inspector.
(6) Subject to the provisions of section 62 of the Control of Pollution Act 1974 and notwithstanding the provisions of paragraphs (1) and (4) above, a person may, between 12.00 hours and 19.00 hours, sound or cause of permit to be sounded an instrument or apparatus, other than a two-tone horn, fitted to or otherwise carried on a vehicle, being an instrument or apparatus designed to emit a sound for the purpose of informing members of the public that the vehicle is conveying goods for sale, if, when the apparatus or instrument is sounded, it is sounded only for that purpose.
37(5) -
(a) used for fire brigade or in England, fire and rescue authority, ambulance or police purposes;
(aa) as regards England and Wales, and so far as relating to the functions of the Serious Organised Crime Agency which are exercisable in or as regards Scotland and which relate to reserved matters (within the meaning of the Scotland Act 1998, used for Serious Organised Crime Agency purposes;
(b) owned by a body formed primarily for the purposes of fire salvage and used for those or similar purposes;
(c) owned by the Forestry Commission or by local authorities and used from time to time for the purposes of fighting fires;
(d) owned by the Secretary of State for Defence and used for the purposes of the disposal of bombs or explosives;
(e) used for the purposes of the Blood Transfusion Service provided under the National Health Service Act 1977 or under the National Health Service (Scotland) Act 1947;
(f) used by Her Majesty's Coastguard or the Coastguard Auxiliary Service to aid persons in danger or vessels in distress on or near the coast;
(g) used for the purposes of rescue operations at mines;
(h) owned by the Secretary of State for Defence and used by the Royal Air Force Mountain Rescue Service for the purposes of rescue operations in connection with crashed aircraft or any other emergencies;
(i) owned by the Royal National Lifeboat Institution and used for the purposes of launching lifeboats.
(j) a vehicle under the lawful control of the Commissioners for Her Majesty's Revenue and Customs and used from time to time for the purposes of investigation of serious crime (which, save for the omission of the words"and, where the authorising officer is within subsection (5)(h), it relates to an assigned matter within the meaning of section 1(1) of the Customs and Excise Management Act 1979" has the meaning given by section 93(4) of the Police Act 1997;
(k) owned or operated by the Secretary of State for Defence and used for the purpose of any activity-
(i) which prevents or decreases the exposure of persons to radiation arising from a radiation accident or radiation emergency; or
(ii) in connection with any event which could lead to a radiation accident or radiation emergency or
(l) used for mountain rescue purposes
