Humm. engine home from Florida huh?
The easy way would be to make sure its drained of fuel and oil and vented for 48 hours prior to shipment. In shipping terms this should turn it from a hazardous good to an innert product. Then you could get it back with one of the main intergrators, (Fedex, DHL, UPS).
If you want to go cheaper and slower the best bet is to try and get it with a groupage consignent as you say. I generally dont use consolidators at work because they dont like carrying my cargoes for security / insurance reasons but would think Schenkers or She Maritime or someone like that would be able to help.
Be careful when you do get it back to make sure you dont get stung for the import duties. if its new you are suposed to declare the value and pay duties and VAT accordingly. if its second hand you need to declare a "realistic" Value but you might get away duty free if you can clame they are british returned goods. (Not strictly true tho!
Remember if you declare a low value for customs your also declaring a low value for insurance so if anything nasty were to happen you are screwed!
hope this helps.