Is a point within a geographical radius - SQL Server 2008

Create Data

CREATE TABLE #Data (
    Id int,
    Location nvarchar(50),
    Latitude decimal(10,5),
    Longitude decimal(10,5),
    Radius int
)

INSERT #Data (Id,Location,Latitude,Longitude,Radius) VALUES 
(1000,'Gloucester', 51.8907127 ,-2.274598  , 20), -- Increased to 20
(1001,'Leafield', 51.8360519 , -1.537438  , 10),
(1002,'Wotherton', 52.5975151,  -3.061798  , 5),
(1004,'Nether Langwith', 53.2275276 , -1.212108  , 20),
(1005,'Bromley', 51.4152069 , 0.0292294  , 10)

Test

Declare your point of interest as a POINT

DECLARE @p GEOGRAPHY = GEOGRAPHY::STGeomFromText('POINT(-2.113189 51.8677979)', 4326);

To find out if it is in the radius of another point:

-- First create a Point.
DECLARE @point GEOGRAPHY = GEOGRAPHY::STGeomFromText('POINT(-2.27460 51.89071)', 4326);
-- Buffer the point (meters) and check if the 1st point intersects
SELECT @point.STBuffer(50000).STIntersects(@p)

Combining it all into a single query:

select  *,
        GEOGRAPHY::STGeomFromText('POINT('+ 
            convert(nvarchar(20), Longitude)+' '+
            convert( nvarchar(20), Latitude)+')', 4326)
        .STBuffer(Radius * 1000).STIntersects(@p) as [Intersects]
from    #Data  

Gives:

Id      Location        Latitude    Longitude   Radius  Intersects
1000    Gloucester      51.89071    -2.27460    20      1
1001    Leafield        51.83605    -1.53744    10      0
1002    Wotherton       52.59752    -3.06180    5       0
1004    Nether Langwith 53.22753    -1.21211    20      0
1005    Bromley         51.41521    0.02923     10      0

Re: Efficiency. With some correct indexing it appears SQL's spatial indexes can be very quick