I tend to leave my car at my garage in the evening and arrange to collect next evening. It'll be first job if the day then. Usually all done by early PM.
£135 for a decent service is a fair price. I'd assume that a set of decent plugs would cost 8x £8 so £64, oil another £30 an oil filter about £5, an air filter about £8. Pollen filters about £20. So assuming all that, you'd be up to about the total cost of the service. I'd assume if that has all been done, the garage has just charged for the parts used and has done it for free. This is good practice by the garage if the customer is left in the lurch. One ****ed off customer can have a significant effect on business. To the original poster, as long as the correct service parts have been replaced, I'd be happy with the job done. The small plugs in a TS are unusual, at 10mm they aren't shared with much else and are fragile in comparison to regular 14mm plugs. Removing it is the garages problem as they are the professional people doing the work. It's only the customers problem if they break them when removing them DIY.
And finally, although some people suggest that Alfas should be treated differently to other brands and given allowances, that's tripe. The TS engine is a clever way to reduce hydro carbon emissions only. No power benefit, the small plug fires to clean exhaust emissions, not improve combustion burn.