A woman sustained fatal head injuries while leaning out of a train window below a warning sticker, an accident report has found.

Bethan Roper, 28, died near Twerton in Bath on 1 December. Her head was out the window of a door when it was struck by a tree branch while the Great Western Railway train was travelling at 85mph.

A preliminary report by the Rail Accident Investigation Branch (RAIB) found a yellow “caution” label above the door said: “Do not lean out of window when train is moving.”

The door was fitted with an opening window to enable passengers to access the handle on the outside.

Roper was onboard the London Paddington to Exeter service returning to Penarth in south Wales from a Christmas shopping trip with friends. The incident happened at 10.04pm and she was pronounced dead at Bristol Temple Meads station shortly after 10.10pm.

Roper worked for the Welsh Refugee Council charity and was the chairwoman of Cardiff Young Socialists. Her father, Adrian Roper, released a statement after her death saying his daughter “enjoyed life to the full whilst working tirelessly for a better world”.

The RAIB said its full investigation would examine the measures in place to “control the risks from persons leaning out of train windows, including the threat from vegetation”.

In August 2016, Simon Brown, 24, a railway enthusiast, was killed while leaning out of the window of a Gatwick Express train near Balham in south London. His head hit a signal gantry at 61mph.

In its report into the incident, the RAIB noted a yellow warning sticker on the door was in a “cluttered environment” among other information signs, and recommended train companies do more to stop passengers putting body parts out of windows.