I have two motorola phones - One that I fastboot erase all'd 'accidently' and lost £300, so I was wondering if I could just transfer the IMEI from one phone to another?
No, you can not move one IMEI to another phone. That number is a lot like MAC address of every device that we use now a days. In theory, and with the help of root. Yes you can change the IMEI. However, that is alot of work.
The IMEI is unique to each phone and is how the authorities can help locate missing phones or even in many cases missing persons.
As for where you might find it. Look in your battery bay. or on the covers. if you have any of the documentation or even the box still.. you can also locate them there.
You can reset or change your IMEI number without rooting your android phone.
Just follow this tutorial -> http://crazytechtricks.com/change-imei-number-android-mobile-phone-without-rooting/
Note: But, The risk is yours. There may be anything gonna happen.