Refer to figure.
Initially, according to the Commission Regulation (EU) No 965/2012 of 5 October 2012, Annex I related to Definitions for terms used in Annexes II to V,

(105) ‘special VFR flight’ means a VFR flight cleared by air traffic control to operate within a control zone in meteorological conditions below VMC.

In addition, according to the Standardised EuropeanRules of the Air (SERA), Annex “Rules of the Air”, Section 5 - Visual meteorological conditions, visual flight rules, special VFR and instrument flight rules, “SERA.5010 Special VFR in Control Zones”, is prescribed that:

Special VFR flights may be authorised to operate within a control zone, subject to an ATC clearance.Except when permitted by the competent authority for helicopters in special cases such as, but not limited to,

• police,
• medical,
• search and rescue operations and
• fire-fighting flights, the following additional conditions shall be applied:

(a) such special VFR flights may be conducted during day only, unless otherwise permitted by the competent authority;

(b) by the pilot:

(1) clear of cloud and with the surface in sight;

(2) the flight visibility is not less than 1 500 m, or for helicopters, not less than 800 m;

(3) fly at a speed of 140 kts IAS or less to give adequate opportunity to observe other traffic and any obstacles in time to avoid a collision; and

(c) an air traffic control unit shall not issue a special VFR clearance to aircraft to take off or land at an aerodrome within a control zone, or enter the aerodrome traffic zone or aerodrome traffic circuit when the reported meteorological conditions at that aerodrome are below the following minima:

(1) the ground visibility is less than 1 500 m or, for helicopters, less than 800 m;

(2) the ceiling is less than 180 m (600 ft).