In any Pongo skin, you will find in the content/speedcam/ folder - you will find 2 UK files

Skin32w_Full_VB_GBR.txt - mph
Skin32w_Full_VB_GBR_kmh.txt
you need to choose one of them,

For versions
iGO_Luna_9.35.2.153810
iGO_Israel(Luna)_9.35.2.263562
iGO_Avic_v9.35.2.227616
iGO_Basar_9.35.2.262743
iGO World v9.35.2.252374
- Skin32w_Full_VB_GBR_kmh.txt

latest version in miles iGO_Israel_9.18.27.955559 - For these versions the file
- Skin32w_Full_VB_GBR.txt

In the next release of speedcam, the file will be called
- Skin32w_Full_VB_GBR_mph.txt
for ease of selection