THE chief executive of multibillion-pound high-speed rail project HS2 has warned that its trains may run slower and less often to stay within budget.

The trains could operate 30mph slower than originally planned, with four services an hour slashed from timetables.

The changes would mean that HS2 fails to smash the 200mph speed barrier, despite costing an eye-watering £56 billion.

The new rail network promised to shrink journey times between London and Birmingham to just 21 minutes, a target that now looks in doubt.

After the inter-city line opens in 2026, the HS2 network will expand north to Crewe, Manchester and Leeds.

The alarming plans to reduce train speeds emerged at a meeting between HS2 boss Mark Thurston and the All-Party Parliamentary Rail Group.

The meeting took place last November but its discussions were only made public this month when Tory Leader of the House of Commons Andrea Leadsom published excerpts on her website.

In a letter, Ms Leadsom noted disapprovingly that HS2 managers believed “a number of changes to the project may have to be considered in order to keep it within budget and on time.”

These included lowering the train speeds, reducing train numbers from 18 to 14 per hour, and changing from slab to ballast track.

Concrete slab track is being used increasingly around the world for high-speed trains as it can handle faster speeds with less maintenance, although it costs more to build than traditional ballast.

Mr Thurston has confirmed the plans existed and reiterated that “it [is] our intention at HS2 Ltd to ensure the project is delivered on time and within budget.”