Car taken after road traffic collision

Hi everyone (England)

Recently I was involved in a road traffic collision. I was the driver and hit a pedestrian who was crossing a country road. The fault lies with the pedestrian but my car was taken for investigative purposes.

I understand the need to check the condition of my vehicle but the problem is I was given no documentation to say it was taken and they have given no time scale to say when it will be returned.

My question is, is this lawful and who would be best to contact to get this documentation?

Thanks in advance