i personally wouldn't buy a CAT D car
1. you don't actually know the full extent previous issue
2. even if you did, the next buyer would be put off
3. even if it looks mint, it can be dodgy as shown on one of Fifth Gear programme with 2 ford focus head on collision
4. the least damage ones would be stolen and recovered, but those have usually seen a hard life when stolen, smoked in, bruised, battered etc.
save a little more or go for something else within budget