1. A method of processing virtual machine instructions, the method comprising the steps of: identifying a subset of virtual machine instructions the processing of which is conditionally dependent upon the value of a condition control variable; fetching and processing a range of the virtual machine instructions into native instructions executable by a processor, wherein a virtual machine instruction counter is incremented after processing and dispatching to the processor for execution a virtual machine instruction of said range, and continuing until a member of said subset of the virtual machine instructions is encountered; initiating a control value retrieval process upon encountering said member, by dispatching native instructions represented by said member to the processor for execution; and processing a speculative sequence of virtual machine instructions when an assumption has been made for an assumed value of a real value of the condition control variable, by: switching a speculative mode switch on; updating the virtual machine instruction counter according to the assumed value, so as to process into native instruction each virtual machine instruction of said speculative sequence of virtual machine instructions, incrementing the virtual machine instruction counter and dispatching the native instructions after each virtual machine instruction is processed, until the real value of the condition control variable has been received; comparing the real value to the assumed value; and reversing the processing of the speculative sequence of virtual machine instructions, purging a speculation mode history, and reversing the update to the virtual machine counter, if the real value is not equal to the assumed value; or switching said speculation mode switch off and purging said speculation mode history, if the real value is equal to the assumed value; delaying further fetching and processing of the range of the virtual machine instructions until the real value of the condition control variable is received and then processing the next virtual machine instruction according to the real control value, if no assumption is made for the assumed value of the real value of the condition control variable.