Insurance is different for every single person.
It depends on the following:
Your address
Your age
Your driving history (how long you've had your licence, any NCB, any claims, any convictions)
Your car
Your use of the car (commuting, business use, annual mileage)
How much a specific insurance company have paid out on people with similar circumstances as you.
What way the wind is blowing.
OK, maybe not the last one, but car insurance is something to no one can really recommend, due to the varying number of different possibilities.
The only way to ensure you have the lowest insurance quote is to contact each company individually.
With the Admiral group (Admiral, Bell, Diamond, Elephant), try adding a middle-aged female as a second driver, that may bring it down a little.