I've added the parties and constituencies they represented to the list of sitting British M.P.s.
....A return has been laid upon the table of the House of Commons giving the names of the peers and members of Parliament who are at present serving, or are under orders to serve, in South Africa. The details are supplied by the War Office pursuant to an address adopted on the motion of Colonel Milward on February 22. The following is the complete list :—
HOUSE OF LORDS.
Earl of Airlie, commanding 12th Lancers.
Earl of Albemarle, lieutenant-colonel, City of London Imperial Volunteers.
Lord Basing, major, 1st Dragoons.
Lord Castletown, special service, South Africa.
Lord Chesham, commanding a battalion of Imperial Yeomanry.
Earl Cowley, lieutenant, Imperial Yeomanry.
Lord Denman, lieutenant, Imperial Yeomanry.
Earl of Dudley, D.A.A.G. for Imperial Yeomanry.
Earl of Dundonald, C.B., major-general, commanding 3rd Brigade (Natal) Cavalry Division.
Earl of Dunraven, captain, Imperial Yeomanry.
Earl of Erroll, special service, South Africa.
Earl of Essex, second in command of battalion of Imperial Yeomanry.
Earl of Fingall, lieutenant, Imperial Yeomanry.
Lord Kitchener of Khartoum, G.C.B., K.C.M.G., Chief of the Staff.
Earl of Leitrim, lieutenant, Imperial Yeomanry.
Earl of Longford, captain, Imperial Yeomanry.
Lord Lovatt, captain, Lord Lovat's Corps.
Duke of Marlborough, staff captain for Imperial Yeomanry.
Lord Methuen, K.C.V.O., C.B., commanding 1st Division in South Africa.
Duke of Norfolk, K.G., captain, Imperial Yeomanry.
Lord Roberts of Kandahar, K.P., G.C.B., G.C.I.E., G.C.S.I., V.C., Field-Marshal, Commanding-in-Chief.
Lord Romilly, special service, South Africa.
Lord Rosmead, major, 6th Battalion Lancashire Fusiliers.
Duke of Roxburghe, lieutenant, Royal Horse Guards.
Earl of Scarborough, second in command of battalion of Imperial Yeomanry.
Earl Sondes, lieutenant, Imperial Yeomanry.
Duke of Westminster, A.D.C. to Governor.
Lord Wolverton, second lieutenant, Somersetshire Yeomanry Cavalry.
Lord Zouche, lieutenant, Imperial Yeomanry.
HOUSE OF COMMONS.
Mr. W. Allen, trooper, Imperial Yeomanry. (Liberal, Newcastle-under-Lyme)
Hon. A. B. Bathurst, captain, 4th Battalion Gloucester Regiment. (Conservative, Cirencester)
Colonel A. M. Brookfield, commanding battalion of Imperial Yeomanry. (Conservative, Rye)
Lieutenant-Colonel R. G. W. Chaloner, commanding battalion of Imperial Yeomanry. (Conservative, Liverpool Abercromby)
Hon. T. H. Cochrane, captain, 4th Battalion Argyll and Sutherland Highlanders. (Unionist, North Ayrshire)
Lord A. F. Compton, captain, Imperial Yeomanry. (Conservative, Brentford)
Viscount Cranborne, commanding 4th Battalion Bedford Regiment. (Conservative, Rochester)
Mr. W. Bromley-Davenport, captain, Imperial Yeomanry. (Conservative, Macclesfield)
Sir J. Dickson-Poynder, lieutenant, Imperial Yeomanry. (Conservative, Chippenham)
Viscount Folkestone, major, 1st Wilts Volunteer Rifle Corps. (Conservative, Wilton [Wiltshire])
Mr. W. R. Greene, lieutenant, Imperial Yeomanry. (Conservative, Chesterton [Cambridgeshire])
Hon. I. Guest, lieutenant, Imperial Yeomanry. (Conservative, Plymouth)
Mr. G. Kemp, captain, Imperial Yeomanry. (Liberal Unionist, Heywood)
Mr. E. H. Llewellyn, major, 4th Battalion Somerset Light Infantry. (Conservative, North Somerset)
Mr. H. L. B. McCalmont, commanding 6th Battalion Royal Warwick Regiment. (Conservative, Newmarket)
Mr. F. B. Mildmay, lieutenant, Imperial Yeomanry. (Liberal, Totnes)
Viscount Milton, lieutenant, Imperial Yeomanry. (Conservative, Wakefield)
Mr. D. V. Pirie, with Remounts Department, South Africa. (Liberal, Aberdeen North)
Lord Stanley, special service, South Africa. (Conservative, Westhoughton)
The Keighley News, Saturday 5th May 1900
Sam Hughes was Conservative M.P. for Victoria County in the Canadian Parliament, and served in the war.
Because of his active service, William Allen (Newcasle-under-Lyme) lost his seat in the 1900 General Election.
Any other active service M.P.s in Canada, or Australia, New Zealand, South Africa?