It was MK1 Equipment that had Auxillary Catenary wire.
To achieve either of these higher speeds, the auxiliary wire will be removed from Mark I OLE at the same time as the contact wire and all the droppers are renewed. The catenary wire will not be replaced, even at 225 km/h, because there are no dynamic changes. This simplifies the upgrade, because unlike the contact and auxiliary wires, the catenary wire passes over rather than under the portal structures typically used on four-track sections.
The cross-section of the hard-drawn copper-silver contact wire will be increased from 105 to 120mm2 in order to accommodate the rise in tension from 10 to 14 kN. This will also offset the loss of conductivity in the former auxiliary wire.
Another important modification that applies to Mark III as well as Mark I OLE is replacement of the cantilevered registration arms - this is already in progress north of Weaver Junction. The new, lighter assembly using aluminium tube and polymeric insulators has a haunched profile, which allows the pantograph greater uplift. The contact wire stagger will be reduced to minimise the risk of dewiring
Taken from Railway Gazette.