Struggling with getting a total from component column

Hi masplin 

A quick fix would be to create another measure Won Value £ summed that iterates over SalesStageSort, summing Won Value £ for each row, and use that in your visuals:

Won Value £ summed = 
SUMX (
    SalesStageSort,
    [Won Value £]
)

or you could include the code from the original measure wrapped in CALCULATE (or some variation of this):

Won Value £ summed = 
SUMX (
    SalesStageSort,
    CALCULATE (
        // Original Measure Expression here
    )
)

Alternatively, you could create a "dynamic segmentation"-style measure similar to the last measure shown in DAX Patterns: Dynamic Segmentation.

Here's how I would write it given my understanding of your model:

Won Value £ (Dynamic Segmentation) = 
VAR Maxdate = MAX ( DateTable[Date] )
VAR DateRange = VALUES ( DateTable[Date] )
VAR OpportunityLatestStage =
    CALCULATETABLE (
        INDEX (
            1,
            SUMMARIZE ( 'Sales Process', 'Sales Process'[Stage Rank], 'Sales Process'[Sales Stage At], Opportunity[Opportunity ID] ),
            ORDERBY ( 'Sales Process'[Stage Rank], ASC ),
            DEFAULT,
            PARTITIONBY ( Opportunity[Opportunity ID] )
        ),
        KEEPFILTERS ( TREATAS ( DateRange , Opportunity[Close Date] ) ), -- Close Date filter
        KEEPFILTERS ( 'Sales Process'[Completed Date] <= Maxdate ), -- Completed Date filter
        ALLSELECTED ( ) -- Optimization to reuse cached results. OpportunityLatestStage table should be computed once.
    )
VAR OpportunitiesInStage =
    FILTER (
        OpportunityLatestStage,
        VAR StageForOpportunity =
            FILTER ( SalesStageSort, SalesStageSort[Sales Stage] = 'Sales Process'[Sales Stage At] )
        VAR IsOpportunityInStage = NOT ISEMPTY ( StageForOpportunity )
        RETURN
            IsOpportunityInStage
    )
VAR Result =
    CALCULATE (
        SUM ( Opportunity[Act Value Won £] ),
        KEEPFILTERS ( OpportunitiesInStage )
    )
RETURN
    Result

Do any of these work for you?