If it is only being used as an excavator then no,but if you start to lift rings ect then yes, what are you classing as a mini digger? Under 10tn is a mini digger.

The document stevel has provided is your best source for this but also a point in your statement that needs clarification often in my experience is "a minidigger only used for excavation". Do not fall into the trap of thinking it's what I'm using it for that matters so much as what the equipment manufacturer designed the machine to do and how it has been configured for operation. Two machines on first viewing may appear identical but there are significant differences that are not always immediately apparent between a basic excavating machine and one configured for lifting. A simple answer to your question is, if it does not have a Safe Load Indicator nor marked with a SWL rating then it cannot be used for lifting, if this is the case then no, LOLER does not apply and you should instead comply with PUWER regs (reg6) regarding inspection.